There are two actual skeleton skins, being Jurassic Kog'maw and Cho'Gath, and the splash art for Grim Reaper Karthus has him as a skeleton.
Is the fact that bones are "taboo" is some countries, one big one specifically, a deterrent for making more skeletal themed champions and/or skins?
Human skeletons and guts are not allowed, basically. I believe it's less of an issue with skins, as those can just be disabled entirely without causing gameplay to be different from region to region.
It has more to do with human skeletons,though some developers go the extra mile and take out inhuman skeletons as well.
It is appearantly also ok to depict the grim reaper as a skeleton,which is why the chinese grim reaper-karthus wasn't censored.
