I think it is usually nonrevs. But there are times when revenue pax are listed on both. This happened to me on a recent SFO-HNL roundtrip. I cleared into J and was then listed for F.
On UA 555 ORD-SFO the other night a pax who was listed as upgraded to J also cleared into F. Ahead of me (I was in J on a Z fare, and wound up #1 on the waitlist). I assume he/she was GS. At the time, the J waitlist was over 50 names long, and the F waitlist was over 20 names.