I would expect this to be common at all companies but I know it's true at Hertz:
If you rent an actual SUV class vehicle they do specify AWD/4WD. Most of what they get these days are AWD crossover-type vehicles, but even within that there are varying degrees of capability, and things like Grand Cherokees are a possibility although would be luck of the draw probably in the Standard SUV class. (Sometimes they do have 2WD variants in the fleet, but they will not rent these as the SUV class but instead a regular car classification like full size.)
To a certain degree this is moot though as technically you are not supposed to take the vehicle off road as per the rental agreement. A gravel public road is a sort of a gray area. I've certainly driven rentals on such roads before with no trouble (with a regular car even), but sometimes the rental agreement states it as "unpaved road" which of course depends upon your definition of paved. One could argue that it is paved with gravel if that is the case.
But if it doesn't actually have any paving at all then you would be in the wrong. Basically, don't damage it or get it stuck out there because you'll be in violation of your rental agreement most likely.