If you look on WDWinfo.com, it does say that Wolfgang Puck Express is on the dining plan. It looks like there are four different Wolfgang Puck restaurants.
1. Wolfgang Puck Cafe - Express
2. Wolfgang Puck Cafe - The Cafe (TS)
3. Wolfgang Puck Cafe - The dining room
4. Wolfgang Puck Express (QS)
I'm not sure if the website is accurate or not, but it looks like #1 and #3 do not take the dining plan, but #2 and #4 do take the dining plan.
Someone please correct me if I am wrong!