There is some confusion over if it's possible to have a WWF roster and a WCW roster for some monday night wars action in universe mode. THQ had claimed you could replace raw or smackdown with nitro and have a wcw roster running against the wwf guys on raw.
Some are saying that when they try to make an all caw wcw brand it won't let them with the game saying 'you need a minimum of 15 superstars on a brand' meaning 15 in game people like the john cenas and randy ortons.
Others though say they've managed to get it working by creating a custom brand, putting their caws onto that, then editing Raw in universe mode and setting it so it uses the custom brand for its roster instead of the default raw brand roster.
You can do it yourself in exhibition though no problem at all.