I have Chickens hatched, and Boars, Wolves, and Lox, tamed, and breeding. Skeletons , since they are Friendly , when summoned, using Dead Raiser, say hungry, so, either it is a secret, on what you feed them, or, like OctoberSky says, it is basically a partially finished aspect of the end game content, as you also cannot upgrade many Mistlands / Black Forge weapons and Armor, YET, past level 2.