Is there anyway the admin can approve or disapprove the new memberships?
Is there anyway the admin can approve or disapprove the new members registration before the registration is completed?
User registration is being processed through default WordPress registration system. If you already have a registration approval function in WP then it'll work for wpForo. If you don't have such function please search for Registration activation plugins, they should work for wpForo too. These are two good examples:
Try second one, if the second doesn't work too try to find other plugins or contact to these plugin support, we don't support other plugin issues.