[Al Skierkiewicz]

Eric,
Remember that in a car the frame is not "grounded" it is the common connection for the power supply. It was and is used to make manufacturing cheaper by eliminating the need to run two wires eveywhere in the vehicle. However, things go awry when body parts have high resistance, loose hardware and defective welds. And in a vehicle collision, electrical faults usually serve to stop the vehicle operation, a result we don't want to happen.
The battery is 12 volts and does not produce an electrocution hazard to First participants.
Electrical contact of auto body parts does produce electrical problems in modern day auto electronics. Although "jumping" a dead battery is normally though of as OK, two autos entwined in a collision can cause serious currents to flow in the bodies of the vehicles. If a car battery is capable of 5500 cold cranking amps and that passes through your car's computer instead of directly to the battery as in jumping, your are looking at replacing a very expensive piece of hardware. It depends on the path the current takes.