We have not eaten there since the new year, but previously the sushi menu was specifically not on the dining plan.
The entrees covered were the tempura, the bento boxes, the grilled steak/salmon, and the combination dinners. Some of these include sushi, but it is the typical tuna or salmon nigiri and not any of the specialty maki or the other nigiri options (like eel or ikura). They have the full range of sushi on a seperate menu, to avoid the argument I suppose.
Of course, they will let you buy as much of it as you like oop to go along with your DDP dinner

We usually buy a couple of kinds to share as an appetizer/along with dinner.