I don't understand.....
As a retired Marine and a former officer recruiter (all services' officer personnel policies are derived from Title 10 & 17, USC) I have to ask "If he's already a college grad, why isn't he applying directly for an officer program"? I can tell you, however, that the prior evidence of drug use would be an automatic disqualifer for commissioned service. "They" are totally non-negotiable on something like that.
Also, he is pretty old and the law requires an initial entrant to obtain a commission prior to their 29th birthday. Even if he enlists first, he still has to beat the birthday deadline. Some of the services will grant an age waiver based upon service (a concept called "constructive age"), the Marines didn't....ever. His chances of obtaining a commission AFTER enlisting are zero when you throw in the drug factor.
I can't think of any MOS that would preclude deployment to the ME indefinately. Your hardcore Navy ratings like bosun's mate, or hull technician would keep him from spending any time ashore, but no way to gaurantee where ships go or to ensure permanent shore duty in Wisconsin. Enlistment promises pertain only to initial assignments, after a few months of service, it's "The needs of the service". If he doesn't want to be a man under authority who goes where he's told, then he should seek employment elsewhere.
It's possible that the Navy recently adopted this policy and it just wasn't communicated down to the recruiter. Having someone reapply who was formerly rejected for a positive UA isn't that common an occurance. Did your brother tell the recruiter about this up front? Things slip through the cracks sometimes. It's also possible that since they're making quota, they can afforde to be more choosy.
From my experience, given his age, overeducation for enlisted service, and the drug thing it's not likely that he's going to get in regardless of how unfair folks on the outside may think it is.
Duty, Honor, Country doesn't always include everybody.