I was about to submit a pseudo-speedrun (me just playing the game pretty fast without using too many speedrun tricks), but I realize I used the rocket nozzle trick (where you store rockets and fly into the air). I was wondering if that is allowed?

If it's any consolation, on one occasion I stored pretty much every rocket I could from a full FLUDD, so it definitely didn't give any advantage whatsoever!

you can do what you want if you started the game on your console or emulator without any kinds of cheats or hacks; rocket storage is used in the fastest routes for all full-game categories