I phoned Dollar at MCO yesterday to ask them about the same question as we have booked the all-inclusive carhire with autosabroad for our trip next month.
We're not sure about taking credit card yet (its a bit maxed out...lol) and autosabroad said it would be a problem.
The girl at Dollar at the airport was so helpful. She said that if we have the maximum package - tank of fuel and extra drivers, and we have a pre-paid voucher then we do not need to give a credit card when we collect our car.
All our previous trips have involved credit cards - but one time we upgraded, another we rented child seats and the other two times we had not paid everything before we went.
Cath