Hello everyone, I´m new to the community and i was wondering if it is possible to use gamecube emulatores for the category of all peak races and if so does it apply to all the other categories in this game. Thank you for reading this!

It would be allowed. Most people run on PS2 emulators so GC emulators are fine I believe.

GameCube emu is fine, however keep in mind that it is prone to being more laggy. Also note that any significant lag can make it so your run is invalid for the leaderboards. I'd recommend trying the PCSX2 emulator. You can find a detailed guide for installing and setting it up here: https://goo.gl/x1GmUi

Hope this helps! Let me know if you have any other questions :)