Can i use an emulator such as open emu or is that not allowed

There is currently no restrictions against submitting a run that uses an emulator. That said, the last time I tried using one I had issues with the waterskip stages making it much harder to play compared to console. At one point we had a runner that did play on emulator that didn't have that issue, so YMMV.

I say go for it, but if it's a time decently close to the current record expect it to take a bit to be approved. Just to make sure there's no issues compared to console that could lead to an unfair advantage.

Good luck and have fun!