As District Emergency Coordinator for ARES in Santa Barbara County, I can tell you that the supposedly dedicated OES frequency of 453.600 is not regularly used or used at all. The 800Mhz hospital coordination frequency suffers from poor coverage. In November we had a hospital drill and had operators at most hospitals and clinics. Our communications were far superior to those of the Public Health Department. We have a dedicated radio system at both the PHD and the County EOC. The EOC never or almost never uses their radio system. They also, with the exception of drills, never use ARES. There is a dedicated repeater linked to Ventura (hopefully San Luis Obispo soon) on 145.160Mhz (Santa Ynez Peak) which functions well for inter-county ARES communications. The repeater frequencies are different in Ventura. Not familiar with all of them. May be in the database.
In a real emergency I suggest listening to fire, EMS and law enforcement frequencies. A single OES repeater would overload with traffic anyway even if someone decided to use it.
The situation in Ventura County is different. They do not use ARES per se. They have ACS (Auxiliary Communication Service) under the sheriff. The same is true in Los Angeles County. LAFD also has a dedicated ACS group.
Ventura now operates a coordinated radio system unlike Santa Barbara. We may soon have coordinated fire communications. EMS is countywide now. Law enforcement not for a long time.