The link you show indicates that it can work across a link if there is a SPAN architecture. This is the rule of thumb you should follow. If you can RSPAN or SPAN all the traffic back to your recording server without traversing a router, it should work. Note that there are two main requirements to be able to do this:
1. Switch in question must support SPAN and/or RSPAN
2. Agents to be monitored must not be across a routed WAN link. (For example, if a remote site is connected via T1 and you have a router at either end with a /30 interface, you CANNOT RSPAN across this).
Additionally, the link you showed advises that things will change in a new version of Agent Desktop, but it indicates that the change is for IPCC Enterprise. I assume that since you have version 3.1.3, you have Express.
Good luck,
Jim