Yes daltonsim you are right. It doesn't matter what instrument. As long as its drums, all 3 kinds of grips can be used. Can use your own also. Whatever works best. Never think about which grip is the best or which one to use. Just use the one that works for you, even if people say it's wrong. That's how people achieve individuality and self-exploration.
And yeah it is true that the french grip is used for the timpani, but only because the single stroke roll is highly important in timpani playing. It is in no way exclusive to timpani players. Check out Billy Cobham for some great french grip playing.
The different grips have different pros n cons, but they're really negligent when it comes to real playing. Trust me, you'll change grips without even knowing it.