Hi Allen,
We don't currently have any kind of white list registration support. Maybe at some point we will implement something for this but its not among my top priorities unless someone wanted to sponsor development to make it a priority.
The best suggestion I have for using the existing functionality is to create a role for each team or multiple roles like teamview and teamedit roles and define those roles as allowed to view/edit/create child pages starting at the team page node.
Then you could enable email notification for registration so the admins get an email when a new person registers and could then go and add the user to appropriate roles. You can enable the notifications by putting this in your user.config file:
<add key="NotifyAdminsOnNewUserRegistration" value="true" />
Hope it helps,
Joe