The equal and dyna beads come with o rings that go over the valve stem. That may tell you if there is any powder in there.
The reason you do not need to balance the rear tires, is there much more weight from all the stuff hanging off the back. The weight makes the rotation much more round. But i would rather have them balanced to start with.
I had a hard time getting the shimmy out of my used MH. I had them balanced, rotated, and then finally the equal removed, then spin balance with lead.