I'm talking with a friend and neither of us are sure about this. What did DG change about werewolves and vampires? I always thought the skill trees were added in WITH DG. Were the skill trees already there? If so what exactly did DG change and why is there new achievements regarding the perks?

Yes, Danwguard added vampire and werewolf perk trees. The achievement was added with Dawnguard's release too.