How do you know which ones are headed for a submarine? The military could literally just pick a BestBuy and go pick up a dozen controllers whenever they're at a port.

The manufacturers in China would have to put backdoors into all of them, which would be noticed pretty quickly, and the gain is what? They can control the periscope direction? That would be noticed immediately too.

I'm not saying it's impossible, but it sounds more like a plot device for a "set your brain on the seat beside you" action movie.