I think Kant would take exception to being called an ontological idealist or dualist. There is no dualism between appearances and things in themselves in the Cartesian sense of "dualism", the "supersensible substrate" of appearances is strictly unknowable. On ontology critical Kant remained strictly agnostic, no matter how much it seems he wanted to transgress in the last two Critiques, and especially in the Opus Postumum. "Transcendental idealism" is not a form of ontological idealism, "idealism" refers to the fact that we only deal with reality through the veil of our mental faculties, i.e. it indicates an epistemological position, and it is not epistemological or subjective idealism in the usual sense either.
Attempts to pin Kant down on ontology, like Allison's or Strawson's, are based on interpreting what he does rather than just reading what he says, and such interpretations are of course controversial. This sort of interpretation started with Fichte, who replaced things in themselves with the "positing" of the I, Schelling and Schopenhauer presented a kind of "vitalist" ideal reality accessible through fallible "intellectual intuition" over and above Kant's transcendental strictures. One can see where they might have gotten the inspiration both in young Kant's musings, and by reading between the lines in the Opus Postumum, but Kant is extremely meticulous at separating what drives and motivates him from what he is willing to commit to officially, so I am not sure such interpretations can ever succeed.
As for Hegel, it is even more hopeless to get a straight answer out of him. Perception of Hegel went through phases, in the 19th century he was mostly the restorer of metaphysics in the aftermath of Kant's takedown of it. Marx's take was that Hegel presented the dialectic of society in an idealistic garb, which later morphed into the picture of Hegel the historicizer, and the prophet of social Geist that you mention. There is enough in Hegel to back up both, and his writing style makes it near impossible to refute anything. But both interpretations seem to be self-serving, and kind of sell Hegel short. Personally, I find Pippin's recent interpretation to be the most plausible. According to Pippin, Hegel fully absorbed Kantian implications for metaphysics, but concluded that Kant was not sufficiently critical of his own method of philosophizing and conditions of its possibility. As for ontology, Hegel is not concerned with it at all because his analysis of the said conditions led him to conclude that "determinations of thought" in the end become "determinations of reality", overcoming Kant's limiting of knowledge. Pippin's interview is a nice read.