You need a permit to sleep on the roadside in specific areas of the park. I have slept in non-permitted areas (ie - illegal, non camping pullouts) a handful of times with no hassle and felt safe when this was needed for drowsy driving. I did get woken up and nearly ticketed by a ranger one of those times, which was when someone moved into my site at Emigrant while I was out exploring.
Many beautiful and relatively 2wd accessible areas of the park do allow “roadside” camping without a permit so long as you are more than 1 mile in, off the “main” road. For instance, Trail Canyon and others off West Side Rd, Telephone Canyon, and many others throughout the park.
Check online or with the rangers at Furnace Creek or Stovepipe. Grapevine ranger station is closed/not staffed in 2025.