I can't say that I can see what difficulties would arise with a player using first person. GM posts can be in third person regardless of what perspective the player chooses to write in, can't they? What tense GM writes in probs shouldn't be affected by this. Crimmy's a decent enough writer to use first person to effectively convey his character's thought process. 

So yeah, I'm with Renny on this. I think Crimmy should be able to write in whatever voice he feels suits the character.