This idea, recently propounded by Joe the Plumber, is probably most associated with the folks at Jews for the Preservation of Firearms Ownership. I’m no World War II expert, and this type of historical speculation — if you held everything else constant, but somehow stopped the Nazis from enforcing gun-control laws, what would have happened? — is always difficult.
However, as a starting point, those interested might want to check out this journalistic summary of the history, as well as these two articles by Second Amendment scholar David Kopel.
Basic takeaway: It’s complicated, but preexisting gun-control laws were one tool of subjugation the Nazis used.