Hey,
I stayed here for 2 nights while visiting Zion last October and I would say a 4x4 isn't needed, there is plenty of space for all types of rigs. We stayed here in a 25ft Motorhome and all was fine, depending how close you want/can get to the stream you just need to be careful of your clearance and any low hanging branches that could scratch the sides but except that it's a great place to stay.
All the best and enjoy
Thanks
Jamie