The only fax solution supported with Unity Connection at this point is Cisco Fax Server. That being said you could utilize T.37 to send a fax message to a Unity Connection subscriber at Subscriber@unityServer.Address, if the gateway IP has been added as the fax server in Unity Connection, it should show up in the users web inbox as a fax message since it has the TIFF attachment, understand that this would not be supported by TAC though.
T.37 off ramp/ on ramp doesn't need any fax server. It can handle in bound and out bound faxing from Cisco VG but is not a replacement for a professional 3rd party solution and is meant for low volume solutions
i've configured onramp on GW and it seems with troubleshooting that GW receive fax and forward it to unity connection. On unity smtp connection i've seen that it receive the message but not able to send this message. Perhaps something missing.