When you do the opt in...im sure the ticket purchase is the same...it asks for screen name. This does differentiate as its not asking for a username but basically screen name meaning whats your id sitting at the tables. That's how I read it anyhow cause its same with ACR/BCP where you can have the same username (account id) on both but screen/table id has to be different.

Essentially Username deals with account for the skin in such a case, while the screenname is recognized accross the network and there can't be identical so has to be different on one of them.