The Alert talkgroup is probably used for the initial dispatch, maybe including some alert tones. The Dispatch talkgroup is probably used for units to advise the dispatcher of their status - in route, on scene, in service, etc, and any other operational communication between responding units.
If this is true, you'll be able to hear initial dispatches but not any of the operational communications.
As Milf noted, it's unlikely that an agency will de-encrypt their communications after making the switch. It has happened, but rarely. I'll comment that it's rare for routine fire and ems communications to be encryoted. I'm pretty sure that Colleton county is the only county in the state with that arrangement. Beaufort County encrypts EMS but not fire, while their fire departments do have some encrypted tac and admin talkgroups. Even stranger is that they chose to encrypt fire and EMS traffic but not Law Enforcement.
If you're concerned about it, it's worth a polite letter or email to county elected officials and emergency service leaders in your county.