please I really want to run this game, but I don't know if it is allowed to use an emulator

it depends on the version of your ROM, if it is American you put it on NA N64, if it is from Japan J N64, and if it is European PAL N64

yes they are allowed, all my smash runs are done in emulator, but I recommend using the project 64 1.6 to not have problems with that