Your engine (et al ) is (probably) going to grounded some how some where.
A bonding strap is a good idea.
Now whether the original engineer of your car meant that to be the primary return path or not, I have no idea. But I sort of doubt it.
Is this why you are still wondering?
http://www.forabodiesonly.com/mopar/showthread.php?t=278980&page=2