Hmm i got the tm ferrari f430 wheel and tried it with gt5, it seemed to work kinda, i mean the pedals worked, buttons on the controller were not mapped at all, and the game seemed to think it was a 900 wheel so it's 200 degree motion would not give you full wheel turn even with the wheel cranked over.
This was under the 1.03 patch not tried with the 1.05 one. Are you sure your pedals are hooked up the wheel cause those were the one thing that seemed to work.