While the idea and incentive are great, he's purposely downvoting users who post quality content without any warning and costing them hundreds of dollars.
In the name of stopping the abuse, he's literally attacking those that are not abusing, but are simply uninformed of his new rule. This is a big playground and it is easy for those focused on their own work to miss @grumpycat's new rule. I think a better approach should be taken.
If I were grumpycat, I would at least try to warn these users, and instead of downvoting them, I would go and downvote the obvious abusers that are using these upvote bots.
Also, I'd go after the owners of the bots. It seems some have not really posted in a few days though, but more awareness should be made.
I for one plan on helping with the awareness, in an attempt to help stop him from needing to downvote innocent content creators. It's a very mean approach, it's bullying on a massive scale because he's costing people money.
I get it though, especially when it comes to those upvote bots that are not cooperating.
I just hope that at one point or another he starts downvoting and flagging actual abuse, instead of innocent people, or the community is going to neuter this cat eventually.