It is undoubtedly RWD, I remember reading an article on it. Also remember the orange 06' STI used by the Yuke's team, that too was converted to RWD. With the amount of customization going into these cars its not a big deal to disconnect the front driveshafts. Also I've seen a couple RWD R34's too.
Oh and obviously my favorite car to drift is the 350z and the Opera Z. I am DYING to play the full game, because my Volk GTS rims are in the game!

They are the rims on the Tuned Evo X. I can't wait to buy a Z in the game and buy my rims to put on it, just hope they let you pick the rim color for each model. ALSO I really really hope they will have different offsets for different cars, If I buy my rims I expect to have the big sexy lip in the rear. If it comes with the offsets like on the Evo X I'll cry.