No, there is NO need whatsoever to move a handicapped person to the front of the line. It's entirely possible, even highly likely, that the restaurant needs to be handicapped accessible, under federal, state, and even local law; but that's the only required accomodation. The restaurant does not otherwise need to give the disabled person preferential treatment. That is not required under any law. Some businesses--like airlines and cruise ships--may do this and allow those in wheelchairs to board first; but that's a voluntary policy the business chooses to adopt. Similarly, the restaurant could choose more seat handicapped diners first, but that would be the restaurant's own choice. And to the contrary: if a disabled patron is being sufficiently disruptive or rude or disorderly in demanding special treatment (e.g. doing so loudly and creating a scene), it might be within the restaurant's discretion to not seat or serve that person at all.