Dwarf actors look a bit waif-like, kinda un-dwarfy from what imdb photos show. Not that I don't have faith that they have the talent, but Rhys Davies kinda had the face for it whereas for these other actors, well, I dunno.
Martin Freeman is a neat choice as Bilbo though. I never thought of that but now that I am it does seem to be a role he could probably play very well.