Scott,
The Y'Stone watercraft WERE few and probably ignorant of the restrictions. GTNP, on the other hand, had and has launch and pullouts for small watercrtaft. One "busy" one is at the Jackson Lake dam on the Snake.
Funny you should mention ths Lewis River. My very first Y'Stone fish experience was on that river between Lewis Falls and Lewis Lake. That was at least 40 years ago. I was much younger then :>)

Mark