If you refer to this article from Apple about the drivers that are available, there is a Fax driver listed for the HP Officejet Pro 8500 A909a Series. So the HP web site appears to be correct and Apple Support is wrong (again).
Don't know anyhting about A909a, but it doesn't work for A909g series. If you try to use the fax printer that worked under Lion, it says that additional softeware is needed. If you delete the FAX oru=inter then try to add it to force a new driver selection, there is no Fax printer that appears for the HP Office Jet 8500 -- only the Printer.
You didn't mention anything about the way how you want to setup and use your printer?
If your printer is listed in this article and your printer is connected to your mac directly with USB cable or with USB cable to the Airport Base station, then you need this drivers: http://support.apple.com/kb/dl907
If you want to use your printer via WiFi, then you need to contact with HP as this printer might require additional network setup (so other devices could see your printer) and also software.
Don't know anyhting about A909a, but it doesn't work for A909g series.
That same article mentions there is also a Fax driver available for the A909g and A909n.
If you delete the FAX oru=inter then try to add it to force a new driver selection, there is no Fax printer that appears for the HP Office Jet 8500 -- only the Printer.
Never had a HP, but with my Canon device that supports Faxing from OS X, you see multiple entries in the Default view of the Add printer window. One for printing, one for scanning and one for faxing. When you select the entry showing Fax in the Kind column, the supporting fax driver is selected.
Thanks IWOO !
A driver in that download did the trick! And for the benefit of others, the driver also works if you're connected on a network. It doesn't come up as a Bonjour "Kind" but as an "HP Fax". Ignore the instructions and select it anyway. Works like a charm. Can't imagine why the Apple Technician didn't mention it, or the HP Technician.