Yeah, it looks like the guy in the shotgun position can actually use a shotgun to blast zombies off the car hood or out the side-doors.
I hope you can shoot from multiple positions in a vehicle. Like if you get a station-wagon you can easily shoot out the back of it from the back seats.
The more I think about this the more I think it’s a great idea. Man, in fact I think I’ve always loved co-op/team combat with vehicles since Starsiege: Tribes, and I can’t think of any other games that do it outside of similar online epic multiplayer games.