because there are two parts to this
(a) the actual SCSI commands that go on the SCSI bus, which the open standards define
( B) how you initiate SCSI commands and get SCSI data to and from the bus on a macintosh are defined in the Apple docs.
So if you are building a device to be operate by SCSI, just use the standards.
If you are writing the mac driver, you need both.