I've been in the USAF for 15 years, and I've stuttered for all of them. It's true that they're unofficially disqualified from communications-heavy MOS's/AFSC's, but honestly those are relatively few in the grand scheme of military jobs. That being said, stuttering won't slow their progress. There'll be times when other military people harangue them about it, but the way to beat that: make jokes about it themselves. Once people see it's not a sore spot for them, it loses its attraction. Military people are assholes, so they'll need to out-asshole them. Wat branch are they interested in?