One more example, LoyceV managed the campaign a long time ago, and as far as I know he is still open to such offers. Do you doubt that he would abuse his merit source status by running a campaign?
I'd argue the opposite: a campaign manager is supposed to read many of the posts made in that campaign. That's a great opportunity to Merit the good ones (and remove the users with bad posts from the campaign). That's not Merit abuse, it's doing a good job.
It may mean the campaign manager sends more Merit to users in his campaigns, because he reads more of their posts. But that shouldn't matter much, as there are 100+ other Merit sources too.
To call it Merit abuse, there should be something in it for the campaign manager. Unless you're going to the extremes of Meriting his own alts to join his own campaigns, but most campaign managers would be able to do that without being a source anyway.