According to my contact, they use cell phones almost exclusively. They use the VHF HEAR freqs as a back up to that. They have the County TRS radios installed but "hardly touch them" for Amb to Hosp comms.
Westchester County DES does encourage the use of the TRS TGs for Amb to Hosp comms. They are recorded and available.
I don't know about Yonkers but farther up the Hudson if you routinely show up at the hospital unannounced you will experience the wrath of the nurses.