Doesn't sound right. UL1741 SA is about grid interactivity with the frequency source grid-side
PWs are just pass-through until it islands, so until then Enphase still has to respect grid-rules. The PREPA profile probably allows Enphase to be flexible with the crazy frequencies from the PW in the micro-grid.
I am not an electrical engineer, so I don't know for sure. But this is what Enphase technical brief says:
Point of Common Coupling: When using a Tesla Powerwall, the Backup Gateway becomes the point of common coupling as per standard IEEE 1547. Therefore, it is the Tesla Backup Gateway that must comply with the Utility's interconnection requirements. Any IQ Micros that are connected on the load side of the Backup Gateway do not have to comply with the Utility's interconnection requirements, and their parameters can be set to optimize ESS operation.