Kerry did do officer training before embarking on the Gridley. With a college degree in hand, it would not be unusual for an enlistee to become an officer or go to Officer Candidate School.
True. That's how my Dad did it in the late '50s. He made it to Lt. Colonel.
Did he go to OCS? It would be unusual to be commissioned an officer right after college without something like OCS UNLESS someone H E L P E D push the paperwork through. Doctor's etc, are another matter. I don't recall seeing anything like ROTC or OCS in Kerry's military info. Even OCS requires some enlisted time and a recommendation to OCS.