First, yes there is some precedent that eating establishments must make reasonable accommodations to meet the dietary needs of individuals with disabilities related to those disabilities, when it is not part of a "package" there is quite a bit of latitude on it though since it is not practical for many smaller establishments to address the broad array of needs. Once it is wrapped up in an all inclusive package it is viewed more strictly say on an American flagged cruise line, otherwise it would have the effect of denying the broader accommodation. This all changed in 2009 when ADA included many disabilities related to the digestive system into disabilities in the law. Yes it is not about proving "better" food, but the same level of food that the person can consume, so with a disability you are not going to get 4 star dining in a 2 star restaurant as part of the accommodation. Restaurants make a choice as to what they include on a menu based on demand of the majority, that is why the minority (with disabilities) have some protections albeit they are often very limited. All I can tell you is to call your regional OCR office and read what I have outlined and you will find out that it is because it is required as part of a group "accommodation" that it becomes an issue. You do not have to use WDW just ask generically. It takes years of experience to understand the intricacies of this area of law, and even then there are gray areas, and this is one of them that could be challenged. It is funny in the OP's situation, that WDW's strongest defense is the DDP adds no value over al a cart, so they could argue that they should be held to the less strict standard (the group will not be incentivized to exclude the person with a disabilities from their plans which is likely the discriminatory impact that a judge would in the end rule on)