As you may know MapWorkshop is now available in CSGO. It really eases the distribution of maps, but also it grants Valve some rights over your work.
I’ve just read the legal conditions and seem rather abusive. They grant themselves rights not just for CSGO and workshop distribution but anything else they’d please, even commercially, different game or not game related. It states it is royalty free and for the eternity, though there might be a payment if your items are sold separately though (I guess hats, not maps).
I’m not familiarized with USA law, but in my country that would be null and void.