Yes.the concern with a "floating" building using a block foundation is usually related to sinking not floating up,except in extremely high winds.my experience says your idea is ok.what part of tx are you in?im in Briar,northwest of ft.worth.
Your idea is fine to set posts.ive built lots of decks onto big triple wide mobile homes with never any problem.the roof is connected to house and posts are concreted in.a whole lot bigger scale than your chicken coop would ever be.