So, I am curious. If Liatris is hardy to zone 2, why does my package state that I need to wait until after the last frost to plant. Is this just to protect new shoots?

Yes !

Thanks! BTW, I was given a different batch that were nearly bone dry back in late October. Can Liatris bulbs dehydrate that much and still be viable?

"Most" bulbs are usually dry and hard when purchased or passed on from a friend.
I've never grown Liatris so I don't know what they look or feel like when dormant.
Many bulbs, if left unplanted for too long, will start feeling soft and spongy and more than likely won't grow. Skipping an entire growing season w/o being planted will render them not viable.
Hopefully, someone who has experience growing them will respond to your question better than I can.

If I remember correctly, the bagged bulbs I bought were dry and kind of wrinkled. I planted them in my gardens and they returned and bloomed for several years, before dissapearing