I believe they operate on the respective division frequencies through their assigned precincts, housing service areas & transit districts, I can't confirm or deny this rumor but I heard that HWY & SOD ESU finally got rid of their auxies, if memory serves me right I believe I actually once saw a mounted auxie in Prospect Park in the mid 70's.
If you care to understand their collective mindset, check out their subforums on these two websites.