You can still charge on your room key, it doesn't matter the type of pass you are using.
I've always used my room key for charging almost exclusively. I figure it's safer than having my actual credit card number all over "the world". Be sure to check the final printout against your receipts. For the first time I had a problem when we were there last month. There was a double post on a charge from MouseGears. We checked out Friday, I didn't notice it until after we left. I called OKW's front desk on Saturday and it was taken off my charge on Tuesday.