A couple points:
If you let them continue, other people might start cheating too and then say it's okay because these two do it and nobody has complained. Plus, these two could become better cheaters.
These two sound really really bad anyway, so I think they're still going to be big donators as long as they keep playing.
So, personally, I would try to get them to stop so long as I thought I could keep them in the game.
P.S. I'll probably be in Vancouver sometime this month and I am a big fish in live games.
