i’ve done a gloss with RR epoxy and it came out pretty good. thinned out the final coat with a little denatured alcohol, sanded to 1000 grit, and polished it up. i was pleased with the result, as was the recipient of the board.
Yes, epoxy will bond just fine to poly as long as the surface is sanded. The rougher the grit, the better the bond (to a degree). Same goes for poly to epoxy. They are unlike materials, so it is a mechanical bond. I just got through adding a poly gloss to an epoxy lam, and it works just fine as long as the epoxy lam is prep’ed right. After sanding (not new, but a whole board restore), I used acetone to clean the surface, because that is what is compatible with what I was fixing to put on (poly). I’m pretty sure the reverse would apply.