Did you try it? My debit card can be "run" as credit, even though it's not a credit card. The money still comes out of my checking account. I haven't tried this with Disney, as I just use a CC. FWIW, online check in is ok, but personally, I've never found it better than regular check in. I don't do it anymore. I did notice before my most recent stay Disney is really pushing it. Anyway, if you can't do online check in, never fear...there are always plenty of friendly CM's at the regular check in counter when you get arrive.