Now if a DT member decides to tag all these accounts( I havent looked at each profile yet to see if that has happened), then I could justify removing all of them for neg rep.
I'd say it's the opposite - even if it's not enough for a DT red tag it should be within campaign manager's discretion to remove accounts involved in merit farming.
The abuse is in the fact that they all send Merit to a 4 year old post within an hour, after which the post is deleted. Although none of that is against forum rules, I'd say it's abuse.
It's interesting that the threads listed in the merit log are much newer than the posts, so the posts must have been moved by a moderator as I'm not aware of a way for a regular user to do that. Perhaps the threads exist in trashcan: