Representative Payee has nothing to do with doing your taxes. It just afirms that the Soc. Sec. monies paid for your spouse were spent on him. You do your taxes the way you normally would.
Yes you still file a joint return. Representative payee is not a big deal. As carosi states--it's just to make sure that the monies are spent on your spouses needs. I don't spend the money any differently than if it was his paycheck. He still needs a roof over his head, food on the table, transportation, etc.....