I was the one that recently tried this. The item rung up and I paid, but the card did NOT activate. If the card is out of their system it won't work. If you try, make sure you get the activation slip from the register and keep it with the card until you use it at the park. Good luck, I hope it works for you!
PS...try to go to the grocery store at a non busy time, it took a while for them to issue a refund for the charge.