In FL Studio's Piano Roll Should My Drums Always Be On Note C5?

Black Panther

grand master
But don't other trap music producers sort of like pitch down hi-hat patterns in FL Studio?

Yes, but that's more like a creative approach which is fine for hi-hats and other stuff although tuning all drum samples will definitely make everything sound cohesive with the music altogether.

It's all a matter of choice and if it sounds good, it sounds good. There no need to follow rules all the time.