Don't know for sure but I don't think so. They probably do some small transaction to make sure the card is valid. On one trip I forgot to notify our CC company that we were travelling and when Disney went to put our room charges through it was declined. Once we put it through in 3 smaller amounts it was fine. To me this suggests there was no "hold" per se.
As the PPs stated, Disney does not put a "hold" on your card. If you have a room only reservation, then the balance owing is due when you check in. Your card would be charged for the full amount at that time.
IF you wish to have charging privileges with your KTTW card, then you would need to leave a cc or debit card number. When the pre-determined limit is reached (as outlined by Missytara) your card is charged, and your limit is automatically reset.
Any additional charges that show up after your checkout will also be charged to your card.
I believe that is for packages. We paid for room, tickets, and dining plan before arrival last November. In May, we had a room only reservation and only paid the deposit until arrival.