Werewolves are legal, but they were released in an expansion pack for the World that didn't come out until well after the events of the games. They did not exist during SIGN.
Er, to tell you the truth, I didn't really understand why they called it DD in the first place. You're not really draining data, but putting people into comas. The term "data drain" would really only work on AI monsters since you're editing their data.
*Insert line full of moral and wisdom*
(The name is ENDER!!!!)