Bingo! Success.
To encapsulate the solution:
1. Set preferred pier side to "east" ( my option for this was found in the "global.h" category found in the IDE software)
2. Make sure the Onstep limits extend beyond the NINA flip trigger (I used 15 degree limit for Onstep, 10 minute delay past the meridian in NINA)
3. It will work if the Onstep auto flip is on or off. Simpler to leave Onstep's off, but if it never reaches the Onstep limits Onstep itself won't ever trigger a flip. NINA will flip before it reaches the Onstep trigger.
All NINA is doing is sending a GoTo to the same spot, so if you don't have east as a preferred side it will basically just stay where it is. If you have east (and of course the pier is before the flip "west") then it sends a goto signal for the same point in the sky, but Onstep thinks it should move to the preferred "east" and the mount meridian flips.