Just had my F150 through Saline Valley and over Steel Pass in November. Listed as most difficult but only used 4WD twice for maybe 200 yards each. (was east bound) These are completely unmaintained roads, go with caution and keep your wits about you. Take a few days rations and water even in Winter.
Saw dozens of Class C RVers in Saline Valley along with many vans and tents. Saw a small plane land on the air strip out there too. Seemed very busy.
Did I mention I love DVNP? Lucky to get out there every couple years.
I think I saw that bolder in the road between Jackass Canyon and Hunter Mountain cut-off. Ranger warned me about it but seemed easy to get around. But conditions can change quickly when there is rain.
Rangers will almost always describe the hazards as more difficult than they are and discourage back country tourism. When I was there NPS was in process of removing a truck high-centered on Lippencott Mine Road. Was a rental and the visitors just abandoned it.