It says that runs must be done on vanilla. Im guessing this means I cant use HoxHud?

Yes, no mods of any kind allowed whatsoever. No texture mods, no HUD mods, no weapon stats changing mods, no skill changing mods, no sound mods, no additional info mods and so on. Nothing that could actually or potentially help you in any way that is not in vanilla version of the game.

ok thanks for that

This includes any kind of mods, even cosmetic mods that don't help you, as they are third-party modifications.