Limpopo
Because the FAA's FAR29 and EASA's CS29 are nearly identical documents, there is no need for the FAA to certify the EC225, in the same way that EASA (or was it the JAA before them?) did not need to certify the S92. They just accepted their FAA opposite number's approval (which in the case of the S92 MGB was probably a mistake!).
I don't know precisely what the process would be, but its likely that the FAA would accept the EASA certification. They would perhaps only want to check that it met the operational rules applicable in the States.
Good for Neill and Dave for bringing some decent large twin helicopters into the Gulf at last!
HC