I would just like to clarify that you mean type 2 diabetes. Just saying "diabetes" doesn't mean much, as people handling food with type 1 very differently. Your best bet at Disney is to educate yourself on food before you go. What foods your body can handle, and what foods cause you trouble. What foods have what amounts of carbs.
You can get a small pocked sized book called "calorie king" , or an app for your phone, like figwee or fat secret, where you can look up the nutritional information on various foods. Disney will NOT provide this information.
As for the chefs, they're pretty clueless. All they understand is "sugar" in relation to diabetes, and sometimes they understand 'bread'. LOL. So a desert with apples still has tons of carbs. They'll simply steer you away from items like cake, and steer you towards fruit. Obviously, fruit is healthier, but often, it has just as many carbs and often it's harder for your body to handle.
And another thing to know is that many people have a LOT of trouble digesting the sugar alcohols in sugar free foods. And many times, those sugar free foods have just as many carbs as the traditional counterpart. They often load up on other products to thicken them and sweeten them.