I have a beige G3, a Keyspan USB Card, and a Epson Stylus 740.
G3 works with 8.6 and the USB 1.2f7 developer drivers. Doesn't work with 8.6 USB Drivers.
Friends iMac with 8.6 doen't work with Stylus 740, but haven't tested it with the 1.2f7 drivers.
I suggest getting them and trying them, I'll be trying it later this week, I'll lets you know how it goes.
It makes you wonder was this thing beta tested :-|