If that is the rule, managers should not look for participants who have posted anything on gambling boards.. because, previous posts before joining the campaign can still be read by anyone here, and what applies is the current active signature. Or another option is to enforce the deletion of previous posts related to gambling for prospective participants so that the campaign platform is completely free from any association with gambling.
Finally, it comes back to prospective participants, if they agree with the rule, take it. If they don't agree, leave it.