I thought I would give everyone an update on this topic -
I tried using my Discover at Carrefour in Shanghai last week. Clerk an the card, but no luck.
I just checked in to the Panglin Hotel in Shenzhen. There is a sign at the reception desk displaying the Union Pay and Discover logos. I handed my Discover to the checkin clerk and she just looked at it, so I turned the sign around and showed her, but she handed the card back and told me to use something else.