I dont see why its crazy to drive from Punta Cana to POP during the night.
Adventurous ? Yes.
Would I let my elder parents do it ? No.
Would I do it ? Yes.
Its not Beirut during the war. No green line here. No shelling.
Its not Bagdad either. No IED's, no insurgents..... that I have heard of.
In fairness, I am pretty sure the car hire place told them not to. They either didnt heed the warning,or didnt understand it. Dominicans are like that.... helpful but overfearful, especially when it concerns tourists.
You don't see why it's crazy, but you wouldn't let your parents do it, and the car rental companies frown upon it. Why? Because you love your parents, and the car rental companies want to see their car returned, and don't want to be linked to any tourists that get robbed or worse. That's being responsible. If you choose to do it yourself, that's your choice, but even though I don't know you, I would attempt to talk you out of it. Dominicans are helpful, but not overfearful as you state, it's their country and they know the dangers and risks of some types of activities.