he must be a Green Card holder with enough time on the card to do all eight years of the intial contract( AD plus any Reserve or IRR time left over) after 12 months in uniform he can waive the residency requirements and gain citizenship. he will NOT be allowed to re enlist unless he has citizenship.
the military cannot and will not help him get a Green card if he doesn't already have one.
Have you read about the Pentagon recruiting non U.S. citizens to join the military? This information came directly from the Pentagon. It also said that 4,000 were non U.S. citizens. You can read more into this if you want to. This is just what I read on several sites.