I have CHF, so it's very important that I limit my salt intake. I emailed special diets and they weren't really much help, they just said most places can accommodate which is sort of true. Be sure to check the special request box on all of your ADR's, this will signal for the chef to come out and talk with him. At Table Service places they can generally make something but be prepared to give them ideas. The only Table Service that was an issue was Garden Grill because it's family style and all prepared in advance. The Chef was ultimately able to get some chicken from Sunshine Seasons and make something. At buffets they will make you something separate so it may take a little longer, surprisingly my best meal was at Hollywood and Vine! The chef there was wonderful and really took time to ask what I liked and find out what I could have. Ohana was also great. Most places will give you plain steamed veggies which gets old after a while. Also, if he's in doubt, don't eat it. There were a few times I got a dish where clearly the veggies were roasted and salted or things were cooked in broth. If he's been eating low sodium a while he'll probably be able to taste it.
Counter service is a bit harder because a lot of it is pre-made and they don't really know what's in the marinades, sauces, etc. The allergy menus they have also don't address low sodium which makes it more difficult. Usually you can get a plain salad and I would also ask for unsalted fries sometimes. Be Our Guest for lunch is one of the few CS that can accommodate low sodium. This trip I plan to do mostly TS and get some groceries delivered so I can make some of my own stuff.