I was thinking the same thing, except with the chat room being 'closed' at all times except when 'scheduled chats' (date and times posted at least a week in advance) were occurring.
Have the same forum moderators (who moderate the forum) moderate the chat room with the chat room only be accessible to logged-in forum members only.
The last Christian forum I was associated with did this where the chat room was open only on Tuesday nights (general chats with prayer rooms or rooms for confidentiality) and on Thursday Nights (prayer only with no generalized chat for the chat room / forums / prayer request threads / prayer request brought up in the chat). Also, if a 'guest' came to the page, he or she could not access the chat room but forum members who were logged in to the forum could access the chat because their name in the chat room would be the same name as their name on the forums.
Surely there is a vBulletin plugin that would allow this with the security features to help ensure some safety to chat room posters