I'm wondering how these solenoids work, and if it's possible to have these function as they would from the factory using the control of an aftermarket stand-alone EMS. In other words, have a completely smog-legal car (well... except the ECU I guess... ).

Please only answer if you know exactly how they work.

 

Your question is a tad vague. To answer it literally, they are 3-port solenoids with a common port, a normally open (NO) port and a normally closed (NC) port. When you apply 12V to them the NO port closes and the NC port opens. But I don't think that's actually what you wanted to know...

There is no aftermarket ECU that could control the entire emissions control system. The stock ECU uses very specific programming to figure out when to operate all the various parts, and in a myriad of combinations depending on operating conditions.

 

Check out the "fuel & emmissions" section of the service manual.
It's all there.
I have a mirror at the link in my sig.
Download & print what you need.