The Smarthome I/O Linc is not available until the end of December so I doubt you will find many folks who have used it. Someone participating in the Smarthome beta test program I think has to sign a NDA to participate. That is what I think as opposed to what I know for sure as I am not a beta participant. To your question, EZSrve functions as a Controller and a Responder. You can certainly link a controller to EZSrve acting as a responder. I have done that with several of my Insteon controller devices. It can be defined as Other if the specific device type does not appear in the device type pulldown. Linking EZSrve as a Responder permits an EZSrve Macro to be triggered from an Input state change at the controller, turning on/off an individual device or Group (Scene) of devices. As the general availability date approaches for the I/O LInc details about its actual operation and capability will begin to surface on the Smarthome forum. It happened that way with the Smarthome Motion Sensor. I checked the Smarthome web site and the only doc I could find is the Quick Start Guide. There is a place holder on their WIki for the I/O Linc User Guide but it has no technical detail.
EDIT: There is one caveat. The Smarthome Motion Sensor did not implement Peek and Poke commands needed for EZSrve to create a Scene. If the same is true for the I/O Linc EZSrve will not be able to create links to the I/O Linc.