I had a receiver parked on the listed CC all day yesterday with a yagi pointed up the river. Even when Cohoes was on a call (dispatched in the usual way on UHF and the Metrocell), there was not even a squawk on that channel. All traffic was available on the Metrocell.
Also, I watched the CCs of both system cells with DSDPlus all day. They have never indicated any other neighbor cells besides each other.
It is possible that "site 3" is a gapfiller, but if so, it appears to be running at very low power and/or from a location with limited coverage, and is not completely available from the main system.