It does not use icon as icon but background image from constructed path. So the icon you have declared in nodes html must exist in correct folder and should be usable as image.
I think to make support of some icon set makes another trap in therms of if this is supported, why that is not. So may be not that easy to make some fancy solution here.
I got burned by the alias naming thing once too. I had dropped the alias name into the node html file for the icon name, and the standard name for the given icon was available not the alias. FA web site kind of implies the aliases are always available... not always. Depends on how the developer implemented the FA library.