Cyber Power are most likely referring to laser printers, which take too high a current for most 'domestic' UPS. I've been running an iPF8300 and before that an iPF8000 for at least six years from an APC Smart-UPS 750 with no problems whatsoever; the indicator LEDs rarely go above 40% load when printing, and that only intermittently. Preferring to err on the side of caution, I chose the Smart-UPS because of its pure sine wave output, but as far as I know the cheaper Back-UPS also work without issue with these printers.
The 750VA unit will currently power the printer in standby, and a wireless access point and 5-port switch, for somewhere up to an hour (the UPS battery probably needs replacing by now, though it's showing no other signs of age); more importantly, it allows completion of a print run and a clean shutdown if an unexpected power failure occurs during printing, which was the original motivation for buying it.
I can't comment on operation with a generator as input - you'd need to speak to the manufacturers.