Yes it is an AGL (Airport Ground Lighting) control system from Heathrow. A little bit misleadingly labelled as NATS ATC. Although this system is the interface between Ground control and Air Traffic Control as it incorporates the runway services in addition to the taxiways. Thus ground and air teams both have access to it.
Of course you could steer planes into each other on the ground similarly to in the air. Also similarly: as the two human (for now :-) ) captains are in charge of visually steering, with just auditory recommendation / control from the tower; there is more than adequate redundancy to prevent danger to life.
The big danger, as has been mentioned, is the reduction in capacity - all pieces of the system from check-in to baggage handling are meticulously engineered to maximize throughput. Of course in the legally mandatory failsafe backup conditions throughput is sacrificed for safety.
It could be wildly feasible to imagine a loss of life procedure where every possible dodgy shortcut has been taken: inexperienced pilot, poor plane maintenance, skimping on fuel load for savings, too many fat kids on their mother's knees - then the traffic control falure could perceivably lead to a fuel starved incident.
Otherwise this may explain the lack of visibility to terrorists vs. just blowing them up in the air. Of course there should be a zero possibility and that justifies the FAA raising this issue.