Joe--it all depends on the underlying health condition. My uncle does not own a scooter however he requires one whenever he will have to do a lot of walking such as visiting a museum. In these cases he rents one. He has neuropathy in both feet and is unable to walk long distances. While he isn't into the hobby and doesn't attend York, I'm sure there are those in the same position.
As for myself, I have disc issues with my back. I could easily see someone like myself needing one should my condition flare up as I would never be able to walk the distances required at York. I do know of one person who attends York who uses a scooter for that very reason (though he owns his). While my back issues are not noticeable to anyone who sees me they are very real when the condition flares up. Hope this helps answer your question.
-Greg
