I don't think so. If you want a 110% sure answer you have to ask the ones arranging it though. But I really don't think that the author of the original story (or the artist of the fanart) is selling all the ownerships to the piece. The one who 'wins' the bidding is just allowed to describe what (s)he wants and will then get the artwork as some sort of present. But of course the original maker needs credit for the work done. If you want a more intelligent and clear reply you can ask the ones who are arranging it still x)