A whitelabel wishlist system can have an unlimited number of administrators. Administrators are simply users of the whitelabel with additional privileges, so that they can log into the Customer Service backend.
To create a new administrator:
1) Have them create a standard user account via your whitelabel. For example, if your whitelabel is at http://mystore.wishpot.com/ - have them click "Create a List" and sign up as a normal user would.
2) In the back-end, an existing administrator can search for a user and upgrade them to administrator status:
The newly promoted administrator may have to log out and log back in before they will have access to the Customer Service panel at http://www.wishpot.com/cs/