I saw in the rules the RetroArch is banned as an emulator, but RetroArch is a frontend that can use other emulators like SNEX9X. Is using SNES9X as the emulator under the RetroArch GUI also banned? I couldn't find anything to clarify this point.

I’ve been wondering the same thing

I looked at the MTPO rules and they banned it because it can alter the way the game plays, so that makes sense to me, and I would assume it's the same here. Time to find an alternative.