I hope so, but i'm not so sure. EA has porsche exclusivity for need for speed, and if forza3 wasn't much of a threat for nfs because was a different style of racing game. Now, there's the nfs shift series, which is a competitor of gt5 and forza, so it wouldn't be a big surprise if EA stopped "renting" the porsche license to Turn10 (like I believe it happened in forza3), just to keep it to Shift. Remember that there's no Porsche in GT5 already, and most of the times, if there's a RUF, there's no Porsche (PGR series for example)
But anyways, we're still a long time from the game launch and I might (I hope I am) be wrong