This is in fact illegal.
However, chadz could likely purchase the rights from Taleworlds to make money off of his mod. Though, I doubt he would do this.
Make all the justifications and relations to other games you want, it is illegal in the case of Mount&Blade: Warband.
An example of this is With Fire and Sword. It is produced by a company named Studio SiCh. Because use of Mount&Blade's features were used Taleworlds was listed as a developer. This is why any use of WFaS content in Warband mods and vice-versa is copyright infringement.
With Fire and Sword started out as a mod, much like cRPG, but then they entered into a software agreement with Taleworlds that allowed them to sell their game independently. They both share the "Mount&Blade" prefix, but have no trademark relation.
Gathered from:
Also, "Oh lets just say its rewards for people who donate.", is a pretty unlikely solution as it comes with a league of legal issues. Ultimately any sort of pay towards the developers of cRPG through donations would be out of the question. Maybe if all donations are shown and reported as going to servers and whatnot, they could get away with it.. still, they'd likely have to consult a lawyer about it first.
I've played a few mods for HL2 and CS that offered Premium Memberships. Those Mods are still in existence, why would this be any different?
Because they are created by different companies..