Shure, the ACDs cannot see the agents at the remote site. They just get messages from the broker when there is an available/reserved resource at the remote site, which was previously selected in remote incoming cct.
I dare to bet it might even work with "select trunk", too

Just kidding... even the broker does not know about any Agents. I used a variable to transfer the desired extension to the remote incoming cct...
I just tested the "select extension" scenario to prove it works. The test-routing is already deleted and meanwhile both ACDs are running run 9.0. But if you tell me where to send the ccts , I'll search in my "sent mail"-folder at work tuesday.
What do you want to use the select extension step for?
It makes sense if you want to queue calls locally and just an additional single agent at the remote site.
To call/transfer to individual remote agents, I would use
network acces codes and the usual select extension step in the default cct of the incoming trunk group at the remote site.