We've had this disussion once or twice before
There is a misunderstanding about whether hire companies 'accept' external insurance or not. This is not an issue: you either buy your insurance from the hire company, or you buy it from elsewhere. If you buy your insurance from elsewhere the hire company will require a deposit from you in case you damage their car. This deposit is taken by way of a credit card imprint for $1,500 (although I have not always been asked to do this). There is nothing in law which compels you to buy the (IMHO overpriced) insurance offered by the hire companies, and if any travel or hire company tries to imply this they are being "economical with the actualité". Therefore it is not up to the car hire company to 'accept' or 'not accept' whatever cover you decide to take out. Technically you do not need to buy any insurance at all (the car hire comes with the legal minimum) but this would be foolish given potential costs of healthcare or legal action.
I've used the Amex policy for the last five or six years without any problems, using Dollar, Alamo, Hertz and Budget car hire. On each occasion I have said that I am declining the insurance they are offering, and this has never caused an issue.
There were a number of examples a few years of tourists being given the hard sell by hire or travel companies to buy insurance, but I think this practice has largely stopped (upgrading your car is another story!). I have never been given the hard sell when collecting a car, at Orlando or anywhere else in the US. Recently, however, a Travel City Direct rep tried to give me a story about Dollar "not accepting" my insurance. I politely told her she was talking rubbish, that I had declined Dollar's insurance on a number of occasions and if she continued to tell me that I "needed" to buy this insurance I would phone my local Trading Standards office. She backed down.
As far as I know there is no other
travel insurance policy which also includes car hire. Alternatives include the Natwest scheme (if you use a Natwest card to pay for the car hire) and there is an insurance company which offers car hire cover in the US as a seperate premium. For us, the Amex policy has saved many thousands of dollars over the years. We normally take the 'free' car hire that comes with flydrives, and that has worked out to be the cheapest option for us. Other people have reported here that they have found it cheaper to buy lower priced insurance and take out all-inclusive car hire seperate from their flight arrangements. As ever, do the calculations and go for whichever option works best for you...
Regards
Rob