I have to add something to what Roger said. You can add as many Publishers in the same network, however they will belong to different CUCM clusters. Once you add the second Publisher, it means that you created Cluster 2, when you add the 3rd Publisher - Cluster 3 and so on.
In the same cluster you may have only ONE Publisher and it is not possible to add another Publisher to the SAME Cluster.
My Cisco Unified Communications Blog