I believe it's called sculling. I don't know if that's just the name of the boat or the actual method but it used to be a very popular way to hunt ducks.
Personally it's not something I think I would ever try (maybe once but wouldn't do it day in and out). The thing that hooked me into hunting waterfowl wasn't big limits and lots of shooting it was the decoying of birds. Nothing is more fun then working ducks into your spread and them having no clue you are there. That's my favorite part and they why I do it.
To Quacks, I would think guys moving around on boats would keep birds moving and would actually help your hunt. Unless someone is rowing across your spread I would say no harm no foul. For him shooting while ducks are working your spread, what is he supposed to do watch your spread and only shoot after? Do you watch him and make sure you aren't shooting while he is sneaking up on ducks? It happens to me all the time on public land. Some group sets up a half mile away and it seems like every time a duck is working "Bam Bam Bam", ducks flair. Then again I am sure I shoot while they have ducks working too. That's just the joys of hunting public land.