I have Atto SE IV in Quadra 800 with mentioned 18 GB Cheetah 15000 rpms disk divided in 5 partitions (partition size with 7.5x is limited to 4 GB n older Macs) and it is perfectly bootable! The only real problem is that you can't install different OS on another partition and choose between them using Startup Disk cdev - all these partitions are visible to it as one disk ;-)

I tried 2.x beta version of SE IV firmware, but after this update ATTO was not visible to ssytem as SCSI controller, so I had to revert to 1.65 firmware :-/