I am running electrical service from one building to another by running two hot wires, a neutral, and an insulated ground wire underground from from building #1 to building #2. Building #2 has a grounding system consisting of a piece of rebar labeled "electrical ground" protruding from the concrete in the foundation. I am not planning to connect the ground bus in the panel in building #2 to the rebar because I am getting the ground for building #2 from building #1 through the ground wire. I have two electricians who disagree with me and say I should run a bare copper wire from the ground bus to the rebar. KISS recently posted a paper by EXACTPOWER which seems to address this problem on page 5 which I thought I could use to defend my position. However the diagram they use to illustrate the problem would have the same problem with or without the second /auxiliary ground rod. I called the EXACTPOWER technical support and talked to an electrical engineer who is an electrical inspector in the state of New Jerjey and he said the diagram was not intended to apply to separate buildings - only an electrical system in the same building. He offered that if I was dealing with two buildings, they should both have their panel ground busses tied to a grounding system at their respective buildings, but that I did not need to run a ground wire between buildings. This seems to contradict what I have read in the ASKME Help Desk answers. Can anyone clarify this for me? A reference to a paragraph in the NEC would reallybe appreciated.

If the rebar is existing in the structure you MUST connect to it. This is a concrete encased grounding electrode, NOT an equipment ground.
A concrete encase electrode is better known as a "Ufer", named after it's inventor.

The ground wire run with the feeder serves a completely different purpose than a grounding electrode does. You need both.
The two electricians you spoke to are right.

The engineer/inspector is not up to speed, or using the 2008 code. The three wire feed to a separate building went away.

Separate bldg needs a grounding electrode.

Do I also need to drive two ground rods and bond to them? This was suggested by one of the electricians who had no knowledge of the existence of the rebar.

No. With a Ufer, no supplemental (additional) electrodes are required.