I am sure there are rules that campaign managers follow to prevent that from happening. But even if there weren't, I am sure such a participant would be asked to adjust his sig and get rid of the warning. If someone is willing to advertise a scam site, it seems paradoxical to have a piece of info that says "be careful when playing on this casino because they might scam you".
Well, I meant individual contracts ... and apparently there are enough participants on the forum whose names do not appear in any spreadsheet, nevertheless, these guys wear signatures with advertisements from different bookmakers
(I suspect this is not a gesture of goodwill). As for the regular campaign, you are right, the participant who added the disclaimer will be removed from the campaign.