I know for a fact that you can apply to civilian residencies. In fact, this is what most of the people do. It's not that they prefer them, it's just there are not enough military residencies for all the HPSP and USUHS grads.
As far as GMO tours, I was told the Air Force had completely eliminated them, the Army was on its way to completely eliminating them, and the Navy was the only branch where they might still be a possibility. That was last February and it came from the website, the professors at the school, and the students who attended. Becoming a flight surgeon is a different matter. It is usually highly competitive and I'm not sure, but I don't think you can do it with only one year of Post Graduate medical education. However, as a GMO you will usually only have one Post graduate year of education. That's why most people hate it. You start into a residency and after the first year they pull you into active duty as a "doc in the box" medical officer. This could last for as long as they deem necessary.
One more word to the OP, they will expect you to stick around and talk to the admission committee. They EXPECT you to question them. You need to do this!!!!