The only version of MTPO I can access is on Arcadespot.com but frontends aren't allowed so I just wanted to know why

I believe it has to do with the way they emulate and frames. It ends up not being 100% accurate emulation. The emu's listed in the rules are all great and I would definitely recommend using them over a website. Also take my response with a grain of salt please. I'm not entirely sure.

building off what he said, im wondering if the emulator over at retrogames.cc is allowed. https://www.retrogames.cc/nes-games/mike-tyson-s-punch-out-usa.html

There are 4 emulators listed under the rules tab that is permitted when submitting any attempts. You can use any emulator to play and practice the game but submissions have to be with one of those 4 to be verified.