I think that emailing special services would be very helpful. Your dining reservations will all contain prior information about your dietary requirements. You do not want to take a chance on cross contamination. In the windjammer and other venues, you will likely need to speak to the staff each time you attend. With any premade reservation, the staff will know ahead of time and will consult with you without you having to ask.
I have a DS who is celiac and I have researched this extensively. He hasn’t sailed since he has completely changed his diet, but we have traveled a lot. I find that generally, the earlier the staff is notified, the better the experience will be.