Same issue _ Canadian card holder
I had a similar situation one year ago
Hertz offered me a upgrade at SFO from premium reservation
It was a Jag XE
However, after 2 fun days, I realized that it may be excluded from Amex LDW
I called RSA immediately and the rep told me that no matter how much it costs, the LDW does not cover Jags
So I switched the car immediately (to a infinity q60 sport which is much more expensive than the base XE but covered under the Amex T&C)