Ed,
I don't understand your images that you have posted. What I can make out is that you have a point feature set that contains your CERP projects which has an attribute field that contains the relevant Regional Command. Using the drop down you have created you should be able to select projects that are within a certain RC.
Your regional command feature set is a polygon feature showing the boundaries for each command area so this must be separate from your CERP projects feature set, so the two would have to work independently. Selecting features in the CERP projects by a RC will not also automatically select the relevant RC in the other feature set.
We have quite a comprehensive flex viewer application running down in RC(SW) used by the UK if you want to private message me I can pass on the details of our data manager that maybe able to help you out in theatre.
Regards
Anthony
P.s. I have moved your thread again as you keep posting to the silverlight forum not the flex forum