So, in the scenario, you will want to put your Lab Edge in the DMZ as well. Doing this will allow you to Federate your production OCS and your Lab OCS deployments.
Where I work, we have 2 seperate SIP Namespaces that use completely seperate infrastructures (LCS & OCS) and we do exactly what you are describing. Some specific routing entries on the Edge servers were required, but the internal Federation works as designed & without issue.
Thx;
Rob