Abraham Kuyper (1837–1920) was a Dutch Reformed Theologian and Political, and in his massive three-volume Encyclopedia of Sacred Theology, I've quoted Kuyper's assessment of Hegel and Schleiermacher in regards to Natural Revelation. Beginning with the introduction in John Calvin's Institutes of the Christian Religion, the Reformed Church has defined its epistemology as a dialectic between knowledge of ourselves and the knowledge of God, beginning in neither the prior or the later, but in the thesis, antithesis and synthesis of the knowledge of God and Man. Schleiermacher's epistemology is defined in a famous introductory polemic in his Christian Faith as a dialetic of Feeling that results as the synthesis of Doing and Knowing. Knowing as thesis, Doing as antithesis, and Feeling as antithesis, and therefore Morality was equated with Doing, and Piety was equated with Feeling and therefore elevated above Morality. Many theologians have doubted that there is any such thing as Natural Theology with Karl Barth's Church Dogmatics, and this has been in reaction to Schleiermacher's reducing all theology to the realm of Natural Theology (an excluding Supernatural Revelation according to Kant's critiques). Kuyper believed that Natural Theology was accessible to man, however, the Fall has resulted in darkening our minds and Creation so that man is unable to know God apart from Biblical Revelation, and that at the Reconciliation of All Things when God is All and All, mankind again will know God in his creation.
The following is a long quotation by Abraham Kuyper with his assessment of Hegel and Schleiermacher in respect to Natural Theology:
Though this deeper truth was not recognized by Schleiermacher, the spiritual father of subjective empiricism, and by Hegel, the master thinker, who founded the school of recent speculative theology, they perceived it, nevertheless, sufficiently clearly to vindicate the primordial authority of natural theology. Calvin saw deeper than both, when he compared ectypal theology, as thanks to common grace it still exists in and for the sinner, to a book the writing of which had become blurred, so that it could only be deciphered with a glass, i.e. with the help of special revelation. In this figure the thought lies expressed, that the theology which reflects itself as such in our nature, is ever the real theology, which, however, must be augmented and be explained, and which without this assistance remains illegible; but which, even during and after this help, always remains the true divine writing. So also it is foretold in prophecy, when Jeremiah declared that there was a time coming in which the outward special revelation would be ended, and every one would bear again in his heart the divine writing, and all should know the Lord from the least unto the oldest. This, too, is only the representation that the outward special revelation merely serves for a time, and that it has no other tendency than to lift natural theology from its degeneracy. Natural theology is and always will be the natural pair of legs on which we must walk, while special revelation is the pair of crutches, which render help, as long as the weakened or broken legs refuse us their service. This indeed can be frankly acknowledged, even though it is certain, that as long as our legs cannot carry us we can only walk by means of the crutches, so that during this abnormal condition our legs do not enable us to walk truly in the ways of the Lord, but only our crutches, i.e. not natural theology, but only special revelation. This last point has been less denied than entirely abolished by Schleiermacher, as well as by Hegel, and in so far we deny that the subjective-empiric and the speculative schools, which they called into life, are able to offer us any real and actual theology. But this does not destroy the fact that the motive which impelled them contained an inward truth. After the Reformation orthodoxy withdrew itself all too quickly from general human life. It became too greatly an isolated phenomenon, which, however beautiful in itself, was too much disconnected; and when it undertook to distil a kind of compendium from the so-called natural theology, and in all its poverty to place this by the side of the rich display of special revelation, it belittled this natural theology to such an extent, that rationalism could not fail of its opportunity to show itself and to administer reproof; while orthodoxy, removed from its basis, was bound to turn into inwardly thin supranaturalism with its external supports. Thus there was no longer a scientific theology worthy of the name. All that  remained was, on the one hand, a mysticism without clearness, and on the other hand a barren framework of propositions and facts, without the glow of life or of reality. This was observed with great sharpness of vision by Schleiermacher, as well as by Hegel, and both endeavored to find again, in the reality of life, a δός μοι πού στώ (starting-point) for religion, and thus also for theology. They did this each in his own way: Schleiermacher by withdrawing himself into human nature, as religious and social in character; and Hegel, on the other hand, by extending the world of human thought so broadly, that theology also found a place in it. From subjectivity, i.e. from mysticism, Schleiermacher came to theological thought, Hegel, from the thought of man, hence from intellectualism, to religion. Thus together they grasped natural reality by the two handles which this reality presents for religion. Natural theology includes two elements: first, ectypal knowledge of God as founded in the human consciousness, and secondly, the pistic capacity of man to grasp this ectypal knowledge with his inner consciousness. Hegel made the ectypal knowledge of God to appear in the foreground of human consciousness; Schleiermacher, on the other hand, started out from the pistic capacity increated in the inner nature of man. Hence it is not surprising in the least, that both formed a school of their own, and that only by their initiative theology revived again as a science. They indeed abandoned the isolation to which theology had fled. Each in his way restored religion and theology to a proper place of honor in human life and in the world of thought. By their work the “unheimisch” feeling of confusion in the face of reality was taken away from the theologian; he had again a standing. The thirst after reality could again be quenched. And that even orthodox theologians, whose earnest effort it was to maintain by far the greater part of the content of special revelation, sought refuge in the two schools need not surprise us, for the reason that the strength of each lay not so much in their positive data, as in their formal view, which to a certain extent was also adapted, if needs be, to cover an orthodox cargo. With respect to this formal part, Schleiermacher and Hegel even supplemented each other. If in Schleiermacher’s subjective school theology was threatened to be sacrificed to religion, and in Hegel’s speculative tendency to be glorified as the sole substance of religion, it was evident that those who were more seriously minded foresaw the future of theology in the synthesis of both elements. There were two sides to natural theology, and only in the combination of Schleiermacher and Hegel could natural theology again obtain a hearing in its entirety. But this whole effort has ended in nothing but bitter disappointment. Not, as already said, as though in these two schools men began at once to cast the content of the special revelation overboard. On the contrary, Schleiermacher and Hegel both did not rest content with the meager data of natural theology, but made it a point of honor to demand the exalted view-point of the Christian religion for its own sake, and, so far as they were able, to  vindicate it. What good was this, however, when they were bent on explaining, at any cost, this ideal view-point of the Christian religion from the normal data? They no doubt acknowledged the considerable interval between this ideal religion and the imperfect religions expression outside of the Christian domain, but they refused to attribute this to the supernatural, and thus to what seemed to them the abnormal action of the living God. The interval between the highest and the lowest was not to be taken any longer as an antithesis, but was to be changed into a process, by which gradually the highest sprang from the lowest. Thus each in his way found the magic formula of the process. From Theism they glided off into Pantheism. For thus only was it possible to maintain the high honor of the Christian religion, and at, the same time to place this exalted religion in organic relation to the reality of our human existence. And this was the thing that avenged itself. For from the meager data of natural theology they were not able to operate along straight lines, and thus even these fundamental data were falsified. This became especially apparent in the school of Hegel, when in their way his younger followers tried to systematize religion, and soon rendered it evident that, instead of vindication, the result, which in this school they reached by strict consequence, was the entire undermining of historic Christianity and of all positive religious data. What Hegel thought he had found was not religion, but philosophic theology, and this theology was no true “knowledge of God,” but a general human sense, in which the immanent Spirit (der immanente Geist) gradually received knowledge of himself. This did not find archetypal knowledge in God, but in man, and ectypal knowledge in the incomprehensible God. Hence it was the perversion of all Theology, and the inversion of the conception of religion itself, and both dissolved in a philosophic system.
pages 217-219, Abraham Kuyper, Encyclopedia of Sacred Theology