Been a while since I played with my ProModule. And been a while since tinkering to any extent with Amiga file systems. I seem to remember the ProModule IDE having a unique driver.device to control it, not the normal scsi.device. Perhaps it's a matter relating to that. Sorry I can't give more in depth help at the moment.
Perhaps have a tinker with HDTools/SnoopDos and see what you can work out?