Fanlore (a fannish wiki) has a page on
Pro Author Policies about Fanworks.
Butcher's sample disclaimer shows a lack of understanding of how Creative Commons works... a work released as BY-NC (non-commercial) would mean that, if Butcher used elements of it for profit, he could still be sued. There is no CC license for "the rightsholder of the work that inspired this one can freely use this one." And there's no CC license for "derivatives are okay but outright copies are not," which is getting to be problematic.
However, fanficcers are pretty much able to sort through weird phrasing from authors & publishers and come up with "you can write fanfic; do not make money off my work w/o direct permission; do not cost me income with your fanfic."