My doubts are driven by common sense and nature of defensive roll.
I do believe that avoiding incoming attack interrupts aiming, as well as being under suppression fire affects defender's ability to defend against other attacks (he's busy enough trying not to catch some stray bullet, and if at the same time another folk is shooting at him, defender is in trouble).
Although defending in combat isn't strictly mentioned as action, there are some leads (not undoubted though) to consider such to be action.
For instance, some defensive measures are mentioned as actions (particularly Interrupt Actions) - Block, Parry etc. Those actions use Reaction+Intuition+(appropriate Skill/Attribute), which is much like regular defensive roll (except for adding skill/attribute to dice pool).