We are planning to deploy a ZLM server in a management DMZ to manage devices in the DMZ. My question is:
what is ZLM Management Zone used for? When should separate zones be used? Will servers in different zones be able to communicate with each other?

We have one zone in use already, all servers in this zone are on the internal network. We will have a few hundreds of servers, but most likely under 500.

Currently, our primary ZLM server is managing all the test devices. Automatic pathing takes place everytime the channels are updated.
We have one secondary server managing all production devices, with controlled patching setup.