I thought the whole point of the wolfbrothers was, their soul was, for lack of a better word, welded to a wolves, which allowed them to access both. I mean, Darkhounds were Shadow-twisted souls of wolves, we know this because bodies of wolves were never dragged off or used.

As to whether there's "deerbrothers" or "eyelash-mitebrothers" is another question entirely, but I feel there's enough support for wolves having immortal souls in WoT.

EDIT Now that I think about it, I mean, wolves got called back by the Horn. Yes, yes, BSand, so who knows how accurate that really is, but hey, you know, if the Horn can call them back, that's another point for "wolf souls".