The road network there is a wild mix of smooth asphalt and absolute dirt tracks depending on how far from civilization you go. Paved highways connect the major towns nicely, but reaching those remote tribal locations requires something much more capable. A 4x4 truck with high clearance is definitely needed to handle the gravel roads safely. You can rent a car in Namibia here
https://getrentacar.com/en-US/namibia . A rugged truck will survive those corrugated dirt roads without falling apart in the middle of nowhere. A tight cabin also keeps all that red dust out of your face while driving through the desert.