No Avaya client is required to do faxing through MM. It uses the Microsoft Fax Client, however MM only provides 32bit drivers for it so only 32bit clients could connect and use it.
Now if you were using a 64bit OS (Windows 7 or other Microsoft OS) then you could provide 64bit drivers in the MAS sharing the fax printer but that it outside of what is supported by Avaya. But I have done it, so I know it is possible.