Rick, I believe the medical condition was determined/confirmed by the induction physical. You could have had a doctor GIVE you a medical condition, but that sounds pretty drastic, and I don't know that you would have been able to find a doctor willing to do it.

As to musicians in the military - being sent to a band unit doesn't have much to do with background, unless you play a type of music the military wants and there's room for you. I don't know if there was a country band at that time. There is (at least in the Air Force) now, as well as a bluegrass band, a rock band, a jazz band, a big band band. I knew one guy who played concert harp. I suspect a lot of these came post-Viet Nam. In any case, they'd find out you could play an instrument and gave you the music they wanted you to play.