To quote the release notes for the latest version of vCO/vRO Multi-node Plugin:
The VMware vCenter Orchestrator Multi-Node Plug-In allows organizations to manage environments with multiple vCenter Orchestrator server instances.
As organizations increase their level of automation, they often find the need to deploy multiple Orchestrator instances. With the VMware vCenter Orchestrator Multi-Node Plug-In, administrators have a more efficient way to manage multiple Orchestrator instances from a central point. The plug-in allows administrators to log in to a master Orchestrator server to view the inventories and workflows of remote Orchestrator servers, and to trigger workflows remotely.