My only experience to date with wheel chairs in Shanghai was at Expo last year with my friend's elderly parents. Since they could walk on their own, albeit with great difficulty, things went rather smoothly. I also learned that almost all subway stations have elevator access.

That having been said, it's not a wheel chair friendly city on the whole. For example, the only way for pedestrians to cross some of the larger roads is via stairs and footbridge.

If I were you, I'd seriously consider hiring a wheelchair accessible van for your trip. It shouldn't set you back more than $500. Finding one might require some research on your part, but they do exist.