The supplementary ground must be tied into the system ground. This ground is an RF ground; the conductors between the radio or tuner form part of the antenna's tuned circuit and must be short to be effective. The service ground is usually too far away to be useful at RF.
In reality, he probably wants to set up a ground window or ground plate to form a single-point ground where all of the cables enter the shack. This plate would have all of the lightning arrestors on it and should be bonded to the RF ground as well as the power ground. Ideally, all cables entering the shack should go thru arrestors on this plate.
They may want to look at the tech notes at
www.polyphaser.com for more info on grounding and lightning protection.
Placing a subpanel in the shack is a very good idea; I would use a main breaker to give a single point to shutdown everything in the room (except the lights) in an emergency.
