Yes, you can use Fax Sender GX in this way. It's useful because other users on the network can send faxes without having the modem hardware installed in their computers.
In order to do this, the server must have the appropriate hardware installed, and both the server and client machines must have QuickDraw GX (version 1.1 or later) and the fax software installed. To install the fax software on a client machine, select the "Fax Sender GX Client Software" Custom Install option in the Apple Telecom Installer.
Note: If you are sharing your Express Modem or GeoPort Telecom Adapter on an AppleTalk network, try to minimize the time you spend in Fax preview. While you are previewing, other Fax Sender GX users may be paused.