jg,
As far as how many prior service enlisted people that have become civilian or military aviators- I don't know. I'm one. I was in the Navy from 17 to 21 years old, active duty, then in the USNR while in college, then 14 year break in service, joined the Army National Guard, and currently an old timer SGT 11B.
Do have a college degree, but did not look too heavily into a commission because I just wanted to deploy. Which I did. Spent a year watching sandstorms, camels, and bedouins from an 1151. Not too exciting, which in retrospect was a good thing.
Anyway- thanks for your service my friend, sounds like you've been around a bit. USMC and Army Guard, bad ***. Thank you for doing the Guard thing. My unit has some prior service Marines in it and I'm very glad they are there. You guys know your stuff.
As far as the GI bill- I used that to help pay for college, and also worked at an FBO fueling airplanes. It worked out pretty well because I went to a college that was pretty cheap, in a town with a low cost of living. Middle Tennessee State University in their flight program. That was back in the 90's so I don't know much about what's up with the new GI bill stuff and college costs.
Have used the flight training I recieved in Alaska. If you want to know more about Alaska stuff let me know. There's plenty of info on here about Alaska 135 if you search it out. Don't know anything about the 121 world, besides what friends have experienced and what I've read on here.
I'm not sure what else to tell you except that I know there's plenty of former enlisted people from all branches out there flying on the civilian side.
Good luck in your endeavours.