What pool bullnose coping for salt water pool?

Salt reacts with metals in an unfriendly matter. Just ask anyone who lives near an ocean or in the snowy/icy north where they put salt down to help clear the roads.

With this in mind, I'd choose any bullnose coping that isn't made of metal. Choose a bullnose that is made of plastic, porcelain, brick, natural stone or plastic coping.