From my experience it is the hotel that will pre-authorize the extra percentage for incidentals and not the issuer. The hotels go with the assumption that most folks will use the mini-bar, charge a meal to their room, view a movie, etc. They just want to make sure you have the additional line of credit to cover those charges. Once you have checked out, the pre-authorized amount is returned to your available credit limit. Hotels do this for all types of charge card so if you are planning a stay it's best to use a real credit card.
Again, as I said, when a guest at my hotel showed up with a CC branded gift card and the transaction wouldn't go though it was because of the issuer. My hotel does not put any holds on CCs on file. In this particular case I called the number on the card to inquire and the issuer is the one who told me they hold back a percentage of the transaction. I've worked at the same hotel for almost 4 years now, and stay at 3 or 4 a year on vacations so I do know how other hotels do holds, however I was discussing my experience with a guest's card at my hotel.