Beanie the answer to your question is YES :).. all the DLC superstars work in Universe mode. Though the attitude era guys that are download content you will have to change them over to the regular raw or smackdown because they will be preset for Raw
is War which is not going on in the Universe unless you have changed your shows over. This year also one thing that was changed, instead of putting people in free agent or some other thing if you dont want to use them in your Universe, is to make them inactive,
you do that the same way for changing what show they are on, just instead of choosing raw or smackdown you choose inactive. Hope this helps.