@Hyper Droid makes a very good point. I find this a very touchy subject; I think that mods and EULAs should never mingle, because as the OP said, when it comes down to it, the only entity that can claim intellectual rights is R*. However, I also believe that those who put hours of time and effort into their mods deserve a little glory, perhaps even a payday (I've happily donated to some). Should they charge outright? I don't think so, but I also don't think it's my place to punish them for it. My reaction is to simply not purchase them, though if they keep improving to the point of being bug free and a little less awkward, I might reconsider.
If anyone were to do anything about it, it would be at R* and Patreon's discretion. Ultimately, only R* has any room to gripe anyway, unless of course Patreon and/or Quechus13 pays them royalties.