The basic breakdown for the dining room staff beyond dinner service:
Waiters work breakfast and lunch in the dining room (alternating as "waiters" and "assistant waiters").
Assistant waiters pull extra duty in the Windjammer, and also fill in at room service from time-to-time.
Headwaiters also pull extra shifts in both the dining room and the Windjammer.
Another thing RCI is working on: dining room waiters will take bar orders for their tables. This is to speed up drink deliveries, which can often be delayed when you have one or two bar waiters having to cover whole sections of the dining room. On our last RCI cruise the assistant waiter provided all soda card orders, and our waiter handled all the wine. Soon they will be getting those martinis and bottles of beer for you too.