If you’re using an Ultra Wide SCSI adapter and have a drive or another device with an ID above 7, BeOS R4 won’t see it. Set the unit (NOT the SCSI controller) to something below 7 and it’ll work fine.
This works with the Diamond FirePort 40, at the very least.
If SCAM is enabled and tells you the ID is set to something below 7 it still won’t work and must be hardware set.