It works. You just have to fire up your other controller. From what I saw...if you have an alternate account(s), it's going to ask which one the new player is to play on.
I do wonder though, if you don't have any alt accouts how would you proceed, as in...would it be "username2"...like on WH with splitscreen.
From what I saw...the player (in house) playing with you, doesnt have access to all the sackperson collectibles for dress. This hasn't been totally confirmed though, I did this when I first logged on, and haven't checked if they have access to the new unlockables.
~Goodz~