Is there a common radio frequency that the emergency services use?

There would be too much confusing cross-traffic for a single frequency to be useful to emergency services in their operational roles.

BUT a common frequency is used internationally by Personal Locator Beacons, and their ilk, 406 MHz. Originally, this service used 121.5 MHz, an appropriated aviation frequency, and this was later doubled to 243 MHz. As from Jan 2009, these frequencies have been dispensed with, and now the dedicated satellites listen out on 406 MHz.