I guess the question is, if he plays one game in center and winds up with a good defensive rating (fingers crossed) is there any limit to how much I can play him in CF while taking advantage of that good rating? I've heard horror stories about unrated players in CF dropping balls all over the place.

It might seem like a bit of a cheat to play a guy in CF all year after he only appeared there once in real life, but if there's a right-fielder in the game who could make the transition from right to center it'd probably be Nixon.