well, I am able to reproduce the problems I am seeing with my scanner: I can get it to respond once, ie, use scanimage or one the X frontends to access it. Then it's time to reboot or power-cycle the scanner. I have yet to acquire an image.
Since I assume the hardware is OK (unless as Abel suggests, Apple has done some clever tricks to resolve termination issues in software), I have a couple of options. I could install LinuxPPC and remove NetBSD from the equation, but I don't know of a reliable distro that I can install with a floppy or via NFS (I have no CD burner). I have cross-posted my earlier message with Abel's analysis to the netbsd-macppc list, but I assume folks have more enjoyable things to do on a Friday afternoon than deal with SCSI weirdness.