I am only aware of a VHF FD Coordinators frequency that came on line late 2016. 151.0700 see DB, This was formerly used by the County Probation department. I have monitored activity on this freq especially during large fires in Passaic. Coordinators were coordinating FD Mutual response and staging various response groups throughout the county.
As to an UHF frequency, I am not aware of it, even after checking for licenses under county name.
There are a "million what if's here" It could be they are using seldom used UHF frequency from County Municipality FD or perhaps using a commercial radio company to lease access to a PL/DPL UHF repeater(s). The frequencies would then be licensed to the communications provider. Or they are on a state system.