The answer is, yes AND no.
I saw a genuine disintegrated rear CF diffuser off a 2002 V Spec II N1 (yes that's right, a real N1) and guess what, it's made out of a thick layer of dry carbon fibre on the outside, and some tye of alloy in the centre. Im guessing it's probably aluminium anyway as the diffuser is quite light.
So there you go. I thought they were supposed to be 100% dry carbon fibre but the fact is, they're not.
I will take a pic next time i see that car.