Just out of curiosity, when you use a warhammer and get the kill animation, do you get to jump on the dragon's head like you do with the battleaxe or is it just the spin kill animation that the greatsword has?

I don't know for sure, I don't use 2-hand weapons.... but looking at the 1-hand animations, I'd bet on it being the "jump on head" version. The only "spin" animation seems to be swords.