Naval Aviators

Any civilian pilots ever in the US space program?

Yes, Neil Armstrong.

Before becoming an astronaut, Armstrong was an aviator for the United
States Navy and saw action in the Korean War.

So, then he worked for NACA after getting out of the navy. So, at that
point he was a civilian.

What I meant was: any civilians who were not originally trained in
military flight programs but in rather in civilian training programs.

Harrison Schmitt was mentioned. A geologist. Of course!