Yes, it's a bit of a gamble. I don't think anyone but GOG should approach any copyright holders. I've thought about it too. I tracked down the people I believe hold the rights to Mindrover: The Europa Project, but I haven't approached them. I don't dare. If a possible future deal with GOG should fall through because I screwed up and said the wrong thing... Well, I wouldn't want that.
I think the best we can do is to inform GOG whenever we find out something like this. They may not do anything about it, but that's their choice. They seem to have their hands pretty full at the moment, and they may not want to spend their time going after deals for a single game.