I got this to pick up the correct revision #:
PHP Code:
$url = sprintf('customprofilepics/profilepic%d_%d.gif', $registration['Registration']['user_id'], $vbulletin->userinfo['profilepicrevision']);
..but then it uses the correct revision for the first user for all the remaining users on the page. So if the first user returned is on revision 3 and the rest are still on 1 it uses 3 for all.