The origins for all the important parts will be the same. But I don't think it's fair to tell someone they aren't allowed to add some aspects or characters from the other company into their origins. After all, there's no canon here to build off of. It's player created. You won't be ultimizing or changing the origins like in UDC or All-Star. But if someone wants to make their origin OU-style, I don't think they should be stopped.