I wouldn't add them if it were my tank. I have white clouds and they are very tough little fish, but then they are little fish and goldfish have the ability to eat little fish (not that they are aggressive, just opportunistic). But that being said a white cloud and goldfish do enjoy cooler waters (high 60's to low 70's assuming it isn't a fancy goldfish) so they would work well together in that sense. But white clouds also love planted tanks with a large current in them (they are river fish) and not all goldfish like a large current (pond fish) and eat most plants quickly.
So again if it were my setup I would just have the goldfish, giving it the best home possible as they do live in species only tanks best, IMO.