Street Gear Poll

MOPE
You're not totally correct, but close. When the angles are exactly the same, but in opposite directions, then the vibrations cancel out, and the natural body oscillations (drone) is less likely to be excited.
However it's not possible to run a street performance engine that way. The pinion angle has to be set for worst case situation, which is ;off the line, full-load,full-power,full-traction. This often requires a static rear angle of several degrees different from the front, often as many as 5* different.
Furthermore as the driveshaft speed increases it becomes increasingly more prone to come into the body occilation, and excites the drone.
And then there's those pesky oval mufflers. They love to get the body excited. And the faster the exhaust pulses come into it, the more powerful they become.
There are other contributors to drone as well; tire sizes come to mind and expansion joints in the hi-way.
BTW, a driveshaft can be perfectly balanced, yet excite the body. This is because of the way those pesky(there's that word again) u-joints transmit torque. When the joint is running at an angle, each of the cross-pins has to speed up and slow down on every revolution,and while it's doing this, the pin is moving in a for and aft direction.The more acute the angle, the more the scrubbing motion. This cannot be corrected by balancing, but only by a nearby opposite acting joint. I myself, don't exactly understand all this monkey motion, but I do know how to minimize it.
Getting back to your NASCAR example. Those guys were running flat out. So they can bias their drive-line angles to a much narrower window. And who knows what their car-bodies were naturally oscillating at . And mufflers? IDK. You see mufflers on Petty's Bird?