There should be a restriction so that both of a person's players can't be on the same team, for the sake of avoiding conflicts of interest.
Looking at it GM wise, if I make a 2nd player and he is not on my team when I know there is a way I could get him to my team, I am much less motivated to work on my 2nd player if I am just helping out another team instead of helping out my own. However, if I know that my 2nd player is not allowed on my team, I probably don't care as much if my 2nd player helps out a team in the EU for example. This also works for the people who are super loyal to teams such as the cuffys or jaime's of the world so their jimmies don't get rustled either.