Ive been with YOUI for several years now......ive had no issues with them so far.
Here is what they say regarding offered driving:
Driving Off Road - Am I covered to drive off road or on the beach?
If your car (typically a four wheel drive vehicle) was designed to drive off-road or on the beach, it will be covered. However, you have to ensure that you drive the car only in a manner and under conditions that are within the manufacturer's recommended guidelines, and that you take reasonable care to prevent loss or damage.
I would imagine most insurers are the same.....generally they won't cover you for driving conditions the vehicle wasn't designed for.....being a 4wd vehicle i would say they'd be hard to deny a claim as it is built for 4wd driving.