Actually, the more you get into it, the messier animancy becomes. For example, why can the Devil and the skeletons actually move? I mean, they have joints, but they don't have muscles. Does the Soul move the "body" through sheer force of will? In that case, could the Steward of Head Warden move?
Good point! If they were to go with the "tried and true" D&D approach to animating statues (iirc), then the steward and the head master should be able to move. Since these two don't, and the rusting of the Devil's body seems to prevent her from moving, I'll wager that bound souls can move things in ways these are physically able to move in the first place.
Which brings us to skeletons: No skin, no muscles, no tendons. This means their bones would be able to move in any direction. Crabwalking wildly-flailing skellies incoming Then we'd need more explanations in the style either of "Magic!" or "well, their former movement is imprinted on their non-mind".
But hey, rule of cool - no fantasy game without undead. And I do like the way they handled it in Pillars, what with the descent into mindlessness. No definitive answer here on how screwed the Devil is, though.