I have met people with a coeliac condition at sea and I know that certain Cruise Lines will cater for you. Some however will not because of the fear of being taken to court should there be a mishap. The best advice I can give you is to write but preferably ring the Cruise Line head offices and get a definitive answer then you are sure and you stand a great chance of having a superb gluten free holiday. Best of luck, Neil Dow.
I would write so that you have something in black and white "just in case".