Hi. I saw your review of my Simple Tank Payload add-on over on Orbit Hangar and I just wanted to thank you for the rating. Also, I wanted to answer your question regarding feeding fuel from the tank to the shuttle engines. In short, the answer is no, because the way that the stock Atlantis and David413's Shuttle Fleet attachment systems work, there is no way to transfer fuel from an attached payload to the orbiter. Also, it wouldn't be realistic, since no such equipment exists on the real shuttle orbiter, anyway.
However, one thing you can do is to release the tank payload from the payload bay and then maneuver the orbiter in and dock with it. From there, you can use something like the Fuel Managment MFD to transfer fuel. This isn't realistic, of course, but it's easy in Orbiter. Also, the tank's geometry means it will not be able to dock with the shutle without touching the crew cabin, but it wasn't built for this purpose anyway. Hope this answers your question.