I'm interested in your findings on this. I was getting P0405 as well as others related to flow. I stripped the EGR and cleaned it out to no avail so replaced the EGR. Now I only get the 0405.
http://www.obd-codes.com/p0405
Gives a good diagnosis procedure which I'm going to try.
I also think the feedback wire should only see the return voltage through the sensor (as you suggest), so would be a variable voltage reading (or a simple 0-5v) depending on the valve position.