To add about the blue-and-white G3 and the Power Macintosh G4:
The original B&W G3 does "support" slave drives, but it's often recommended against because it works poorly. The best way to put it is that the second revision of the board "improves" slave drive support and removes an error that could cause corruption if you had a slave drive.
I've never been able to find any reference to any Power Macintosh G4 not supporting slave drive operation, and in fact, my Yikes! G4 board happily ran two IDE devices on each of its onboard IDE channels with no troubles whatsoever.