I'm afraid that aslong as he can prove there was damage, and what all the costs were, yes, he could still have a case.
Recently my OH's BMW was bumped from the back whilst stationary by a guy who freely admitted it was his fault as he wasnt looking ahead.
They inspected the cars, didnt look like there was damage, but swapped details and then left.
When my OH got home and told me, i suggested he take his car to the nearest BMW dealer, just to be sure, as you cant always see the damage from outside the car.
Good thing he did, as when they checked, the bumper bar was actually damaged, and you could feel where it had rippled despite not being able to see it.
If he had been hit from behind again with the damaged bumper, it would have lessened its effacity. So the other driver, having thought he'd got away with it, actually got a bill for about �1600.