I believe this is unlikely to happen. Campaign managers would evaluate this type of situation before approving a new user for their campaign. And even if it was accepted in both, the subscription campaign manager would most likely reevaluate keeping that user in the campaign.
Yeah, I'm sure that campaign managers wouldn't let to advertise two competing business at the same time - you can't sit on 2 chairs at the same time.
But when probably 90% of campaigns is about gambling, it doesn't leaves many options to advertise something different.