Time for me to run Pro96com to find out

It would seem that might be, or, GCPD has De Kalb's TG programmed into their radios.
Larry
Yes the Dekalb TG would be unencrypted. Officers on a federal task force, such as the violent crime task force which is staffed by ATF agents, Dekalb, Altanta, Gwinnett etc detectives (all sworn as federal agents) all have each others radio freq's programmed. There are a ton of feds on all sorts of task forces which have GCPD TG's programmed in.
In the world of multijurisdictional task forces they have tremendous communications capability becuase there are so many local agencies represented on such a task force.
Nearly all the metro 911 centers have the ability to patch talk groups with neighboring counties. I once heard Fulton Co Fire call for Gwinnett Hazmat to go to a call in North Fulton. Gwinnett 911 patched Fire Tac 8 to a Fulton Fire Tac so everyone could instantly talk to each other.
GEMA has a van that can link several types of comms together. You could have 5 officers using VHF, 5 using UHF, 5 on an 800 p-25 system, and this comms can can link them all together on a repeater network so they can all talk to eachother as if they were all on one system. Ive seen this used and it works great.