Well, as an update, there is also an option to launch and run Simulate directly from the desktop, which requires that any changes to the assembly model be done in a separate session of Creo. I have not confirmed the behavior of this approach, but may soon have the opportunity. Specifically, whether the Simulate model updates to reflect recent changes from the Creo session.
With the standalone Simulate session, ptcstatus indicates that I am using an Essentials license, not the Meceng_Advanced as I would have expected. Perhaps this explains why results files have been created, but remain consistently empty!