Have to read two time that you asked a question on "Victory Decision - Future
Combat"...
And yes shooting at the assaulting unit is a valid overwatch action; quote:
"Whenever a visible (not hidden) enemy unit completes an action within 2x the Leadership Distance of a unit on Overwatch, that unit may immediately make a free Shoot or Move action. This is called an Overwatch Action."
BTW - This is another good example how the performance of well trained troops is reflected in the rules.
High Leadership units not only can be wider deployed, are easier activated they also react to during overwatch better!
@pixelgeek: Can you change the Topic subject to: "ViDe Future Combat Overwatch question"
Thanks.