You may in general order anything on any menu at any participating restaurant.
The restrictions usually concern multiple-course fixed price menu listings. Some restaurants do not permit ordering these on the dining plan. Others allow it with a surcharge. One (Le Cellier) allows ordering from their three-course fixed price menu even if you are on the basic dining plan, but they do not permit any substitutions.
For the previous poster: According to the latest reports, Coral Reef doesn't serve lobster. Currently the only place to get a lobster entree on the DDP is Narcoosees. The lobster is not restricted from the DDP there, but Narcoosees is a 2-credit restaurant.