We just got back from our cruise on Oasis and thought we would update this thread. Before eating in the dining room each time we would tell the waiter that she was on a gluten free diet. If the waiter was not familiar with the selections on the menu he would get the head waiter to go over the menu and discuss her options.
We had "My Time Dining" for dinner but always ate in the same spot and all but one night with the same waiter. Each night the head waiter would come over with a copy of the next nights menu and help her choose her meal.
The staff on the Oasis went out of their way to help us and make sure that she got the right foods. The new menu now have symbols for certain diets. But you should still consult the wait staff.
PS - The food was excellent!!!
(gluten-free bread not so much