The Uncanny Valley is an instinctive response to things that reach the "top" of non-human spectrum, and the "bottom" of the human spectrum. In theory this is to avoid disease and deformation. heavily-biologically-damaged humans are "likely" to carry disease or have undesirable genetics. Near-human organisms would be likely to carry near-human diseases that could quickly mutate to affect humans.
"Uncanny Valley" also varies depending on the viewer. If one has a stronger "familiarity" with demi-humans then ones Uncanny Valley threshold, in theory, could lower a bit in regard to the appropriate demi-humans.
This is just my take. Keep in mind that I just woke up, and I'm still groggy.
By the way, nice work on your gallery submissions.