TL;DR That's the problem that stopped me from finishing.
Long: That was the issue that sidelined my progress long enough to keep me from finishing. I understand roughly what the problem was--I built my VR game interaction system around picking up items that exist in the world, not creating and dispensing new items into a hand.
The spawn plus grab causes...unpleasantness. I think it's because the item is kinematic until a grab is triggered, but there is no logical reason why the character Rigidbody should have upward force applied, and it was not nearly so pronounced in the editor so I am guessing it's frame rate dependent.
I'll be replacing the whole interaction system for my next iteration.