Yes, do contact them. You'd be surprised what they are willing to do for you. I had thyroid cancer surgery and had to go on an iodine-free diet for 6 weeks each year. One of our cruises was scheduled during that six week period.
This is a very difficult diet because there is iodine in almost everything that we eat! However, I found a diet book with recipes online. I sent a copy of the recipes to the cruise line several weeks before our departure with an explanation. During that entire cruise, the chef prepared special meals for me for breakfast, lunch and dinner. At one point, he came out to our table to ask how I had been enjoying the meals (he did a fabulous job, all of his preparations were delicious!). He said that he really enjoyed the challenge of inventing meals that were good tasting and had a good presentation and he loved being able to surprise me at each meal! He even figured out how to make some wonderful tasting iodine-free deserts.
The other members at our table even started getting jealous of some of my meals (in jest, of course). I was so impressed that they went through all of this trouble to make sure that I enjoyed wonderful cuisine like everyone else.
Anyway...they will accommodate you in any way they can. Just ask!!
Peace and Blessings
Look For The Good and Praise It!