I have never seen or heard of that marking on any other gun, so if it was a dealer his marking is not well known. I would assume it is the name of a previous owner. Putting one's own name on a gun is not that unusual, but it is more commonly seen as an engraving or stamped with individual letters than as put on by a single stamp. As for proving ownership of the gun by a specific "E.W. Moore" that would require a lot more research. The best evidence would be that stamp on some piece of property that is defnitely known to have belonged to the naval commander. In my experience, people who are into putting their names on things put their names on just about everything in reach, so I can imagine that stamp on sword hilts, knives, leather goods, cap badges, etc.
The name Moore is pretty common; I have known several people by that name and even knew an Edward Moore, but I don't recall his middle name. There was a Moore who patented and made revolvers of the front loading type, but his first name was Daniel.