I'm not one to ever shy away from fatty food, but, on a NY pie, with a quality (read: fatty) whole milk cheese, typical supermarket Italian sausage gives off too much fat. Even when I make my own sausage, I still use very fatty pork, as the fat in the pork, when it renders, creates a juicier and more tender end product.
On Neapolitan, with a usually smaller amount of cheese, and a cheese that doesn't give off a great deal of fat, sure, raw sausage is probably the best choice.