I'd reconsider not hiring a 4x4. We did and had a much more comfortable journey including that road up from Sesriem to Windhoek (which was a pretty long haul on gravel taking us about 6.5 hours).

Friends of ours who'd been there before us hired a saloon and got stuck on that same road, just bogged down in the gravel. The other thing they'd warned us of was the constant noise of the gravel banging against the bottom of the standard car which really got to them. Of course you can't go much faster in a 4x4 but you will probably be more comfortable.

The animals which appeared to most like sitting on the road during the day were baboons but there were others such as ostriches so you probably need to be careful during the day though it's not as much of a problem as at night.

We hired with Budget from Windhoek and they also excluded gravel road cover so I think that's fairly standard.