Can a creature with madness that has been exiled by a source other than the madness affect be cast from exile?

If I had a creature with madness on the battlefield and it was exiled by my opponent with, say, Faith Unbroken for example, could I then proceed to pay the madness cost on that creature? Also, if I were to pay the madness cost would I create a copy of that creature or would I just return it from exile? I've checked MTG wiki but I don't see any rulings that specify what to do in this situation.