This one I need to research. My gut instinct tells me you're right: the doctors drafted to work in Korea came in as Captains (instead of as Lieutenants) for precisely this reason: their MDs. But that was wartime, the draft, and the Army, of course.

Since we see Janet enter the SGC as a Captain, yet she's obviously somebody with enough mojo to be the CMO of a top sekrit MajCom facility, my guess is that she was Out and in civilian life and the USAF pulled her back in for the SGC. They'd have the option of doing so at the rank of her separation (like Jack, the eternal Colonel).

This would fit in with what little we have on her background from "Hathor" -- divorced and entered the Air Force after her divorce. We can presume therefore that the USAF may well have paid for medical school.

Yeah okay, rambling. I'll do some research on that Captaincy thing and get back to you...