"Not all recruiting people are jerks."

Maybe not, but they are under incredible pressure to provide warm bodies to the war machine. Suicide has become rampant among US Army recruiters (expecially in Texas, if that is at all relevant), enough so that the Pentagon and several congresisnoal committees are looking into it. The brief rush of idealistic/"patriotic" volunteerism that occurred in the wake of 9/11 is all over, but the need for personnel is not.

Q's anecdote about Vietnam-era recruiting protocol is irrelevant today. As all of us of a certain age should recall ~ and many of us will never forget ~ that the US military was able to rely upon conscription (the draft) for their cannon fodder back then. Today, the military machine has to rely upon an all-volunteer force, which is why so many young people are being sent back into combat for second, third, and fourth tours of duty.

Your nephew's individual recruiter is NOT going to want hear about any condition that might prevent his recruit from going through with induction. His/her commanding officer might be more responsive, but the CO has quotas to meet, too. If there is an actual documented diagnosis of bipolar disorder, you might consider notifying your congressman.