He might, or he might not. Unfortunately, there is no 'yes' or 'no' answer to your question. It really does depend on the individual personalities involved. Theoretically speaking, the ducks would be no match for the gander. In theory. But that's the problem with theories, they rely on ideas that are generally assumed to be true, but aren't necessarily so. You could end up having the most gentle, laid back gander in the world, or...you might wind up with one that thinks he's Godzilla. You just never know. Like I've mentioned before, all of my animals free range together without major issues, but I could just be lucky in that regard. Either way, I wish you the best with whatever decision you make!