Minor rear vibration.......

That is correct. I am skeptical that a new set of tires curing the out of round issue will be the cure. Not sure how plausible it is for any vibrations from a bad tire to travel up the driveline (driveshaft mainly), in such a manner that I feel it up under my seat and feet, particularly just as I ease of the gas. That being said, I have been told by two shops that at least the right rear is out of round, so they need replacing anyways.

Before that, I might try unbolting the driveshaft and rotating 180 degrees to see what happens.

In the meantime, I have just kept speed under 65mph as much as possible when I drive it every other day just to be sensible.