The point is that if he does so, he's criticizing himself. If you understand that Clinton only acts in his own interest, you see that this is a way to make his interest Bush's. It won't make criticism impossible, just difficult.
In what way? He can criticize FEMA and the Federal response while portraying himself as just trying to help raise money for a worthy cause.
I just don't trust this man any further than I can throw him, and I expect you don't either.