Interesting. It's something similar to moral licensing, isn't it? I've done good now, so I have the license to not do good later.
But to me, this thesis has one glaring hole: the states of affairs brought about by the offsetting seem incommensurable to the states of affairs brought about by turning vegan. That is, we're comparing apples and oranges. Money and harm seem to be incomparable in any way. That's why we have the death penalty: it makes crime and punishment commensurable. I agree that compensation and retribution need to be implemented. But money seems like something incommensurable to moral values and I don't think the consequentialist will advocate this as well.
Theoretically, I think this system will create an extremely dystopic world where the rich are allowed to commit all sorts of heinous crimes. Today, we start offsetting rape and meat consumption, the next day, we're going to start offsetting murder. Where's the line? So, no, I don't think moral offsetting with money is a plausible idea.
Thanks for the fresh perspective.