For roleplaying sakes, best you can do is be a Vampire with Werewolf Lord Polymorph. That Vampirism is going to restrain, drain and curse the beast inside just as much.
Gameplay wise, the forms work best as supplements of different styles and builds from one another. Unless... This isn't just for adding the Vampire's 10% Stamina Recovery on top of the Werewolf's Stamina Recovery for your Stamina DD, is it?
I might be a little curious what the Volkihar clan may be up to in the 2nd era. Either there's a fun Vampire Lord boss out there somewhere or they are all shut in watching re-runs.