On rental terms here, there is an exception for use on unpaved roads for normal cars for activities such as egress and ingress to national parks and similar
For vehicles designed for use off road, there is no such exclusion and would not be an issue
In this case, it seems that it might be worth popping by the rental office t some point and getting it sorted rather than a holdup when might be in a hurry on return - from what the OP has stated, it seems that Hertz would be well aware of the situation