How have you done that?
Some time ago, i tried that but only found 2 solutions:
1) Syncing the Userdatabases (so you have two Userdatabase)
2) Switching the wohle Usermanagment to Joomla
Because i everthing build around vBulletin, it's no option for me to switch Usermanagment to Joomla.
Have you found a way, Joomla uses the vB
-Userdatabase directly /without sync)?