Rev 1 B&W G3 does NOT support booting from slave IDE devices because the on-board ROM for the controller does not understand how to access slave devices. OS X overcomes this because it loads a software "ROM" to handle the IDE controller. If you want to maintain the ability to boot from CD/DVD, you'll need to set the optical drive back to master.

Rev 1 B&W G3 IDE controllers introduced drive corruption on certain UDMA hard drives. As the ROM for the controller is updated in OS X, it's probably safe to use any drive under OS X.

Rev 2 B&W G3 does not suffer from either of these problems.

All you ever wanted to know: http://www.xlr8yourmac.com/g3-zone/yosemite/IDE/

Peace,

Drew