Here's my question: If I'm planning on playing Dawnguard on my level 80 charater, does this mean I can't level up/gain perks the vampire/werewolf form?

Vamp and werewolf perks are gained through combat in their respective forms as far as I know.

Werewolf vampire perks are completely seperate and earned by kills

I have heard that perks for the vampire/werewolf come come from completing quest lines (unreliable source). But im sure Bethesda took high level players into consideration when making the DLC.

Ah thanks for the replys. I was worried I'd have to start a new chartater after spending hundereds of hours on this one.