If I were your mate, it would be worth completing his CPL before departing for the States. If he has a ways to go, at least get his PPL out of the way. He should easily be able to work towards his FAA CPL Helo based on his private aussie ticket. I whent over there some years ago armed with a PPL Helo and then got my FAA licence.
The events of Sept 11 may have changed how foreign students (green card or not) are handled as regs. may have changed. If he wants to get hold of the regs., contact a reputable flight school or get a copy of the latest FAR's from sportys.com.