We were there 9/10-9/17 and found we were able to get slush drinks in Epcot at the Cool Wash station outside of test track. The lady there originally said no, but the cost was $2.50 and the $2.50 bag of chips was included, so I asked if she could try anyways, and the card went through. Sometimes the CM's do not know, but the fool proof way is to ask them to TRY it with your card.
Same thing for breakfast at the resorts - every morning my husband and I would share the pancake breakfast platter, get a fruit cup as the "dessert" and a water to take to the park; on our 5th day of doing that, the lady told me (in a loud voice in front of a lot of people) to "take that back - it is not included in your meal plan!" when I advised her that I had done that the previous 4 days, she said "it wont go through" and I said "oh yes it will" and she finally tried it, and rather indignantly, I might add. When it did go through, not even an apology!
Long story short - Try it!
