We don’t make that exclusion, mostly because (in our area at least), that would prevent our renters from staying at a lot of very cool nearby campgrounds. We just have a rule in the rules section that it is the renters responsibility to ensure their route can be driven safely without causing damage.
Just as @JordanB said, in our area, dirt roads are commonplace. Here in California, we limit dirt roads to non-fire trails (those should NEVER be camped along, by anyone, ever, but especially during fire season.)
As for basic delivery, we deliver to a lot of boondocking/dry camping sites. There are a lot of dirt and semi-unmaintained roads. My suggestion would be to have your renter (when possible), drive up and down the dirt road they expect you to deliver to and depart from, to try to give you an accurate expectation of the topography of the area.