Oh, did that change? When I went, they said they would accept gift cards and earned rewards (like the free drink on your birthday or stars creating a free drink for you) but said anything you buy would not count toward your star-count. Which made sense as their prices are a bit inflated and that would count toward extra stars.
EDIT: My information is a bit off. I redeemed my free drink at one of them in Disney Springs, which do allow for rewards as they are company-owned stores. Sorry for any bad info I might have spawned.