Assist can do whatever they want, but they have to be careful with what they do. You can't just do whatever you'd like, you have to bear the opinion of your target audience in mind. If I think I have a solid reason to ban someone (in my opinion) from MY server that I pay for and somebody from the development team is forcing me to allow that person to play because they received a little bag of money is ridiculous.
I agree. There should be no reason that the Assist admins should be able to say who you can and cannot ban from your server.
I mean, on your own server you can ban people for various reasons, from excessive (and intentional) TKing to extremely hostile/rude behavior towards others in the server, from exploiting bugs to disrespecting server rules. Now if the admins said you couldn't ban this "ex"-cheater, he'd be at an advantage compared to any regular legit player.
And since usually you're allowed to ban players on your own server, most server admins would probably ban the known "ex"-cheaters.
I'm pretty sure everyone here understand the noble idea of giving this project some much needed cash, but IMHO having cheaters paying to play again is not something that would work.