A u-joint when working at an angle will have fast and slow portions of its rotation, for lack of a better term. The idea is to have these motions in phase w/each other. If there are more than one out of plane angle, it's easy to visualize how there will be problems.
Whether a 'Vette has this "two planes out of phase" is really a moot point. It is not a desirable thing, and I suspect the engineers of the 'Vette did this for reasons that are not usually encountered- and did the things necessary to quell any damaging vibes/oscillations that will result.