The perks are recognition and depending on the length of the cruise, they always have at least one DVC member appreciation event where they will sometimes have free drinks, and virtually always have free DVC caps, and miscellaneous small giveaways.
DVC members can get a special lanyard from the DVC sales kiosk if they didn't see the DVC folks in the terminal to get one, and there are often little giveaways ( I do mean little. Cutesy trinkets usually, occasionally a Disney pin) that are almost daily. It helps drive traffic to the DVC kiosk.