Almost correct, Mike.
It's an EDACS system with analog and ProVoice modulation. Darn near everything is ProVoice which can not be decoded by any scanner. A few talkgroups, like the dog catcher and some other city services, as well as Fire Dispatch (the dispatches only - the rest of the traffic is ProVoice) are analog and can be heard on a scanner.
In summary:
Any EDACS capable scanner can trunk-track the system (i.e. know which talkgroups are active), and any EDACS capable scanner can listen to the analog talkgroups, of which there a few, but NO scanner can listen to the ProVoice talkgroups, of which there are many.