The reference to the Insteon device being linked to the EZSrve is an Insteon requirement. The EZSrve will not receive a device On/Off message required to trigger an Action without that link.
X10 events can be used to trigger Actions. Using the HTML interface I set up an Action triggered from an A05 On. The Action was triggered. I then brought up the Harmony interface to see how it would display the Action. Unfortunately it looks like my Actions file was corrupted and erased when I tried to update and save that Action.
At present my EZSrve is in a reboot loop so I am not able to do more testing. Once I get that cleared up I will come back to this question.