With ELM the license are tied to the ELM node and can be shared by multiple CUCM clusters. ELM will sync with all the clusters and provides an overview of all the licenses being used by all clusters, if you have sufficient licenses installed on ELM then no alerts are generated if not you will see alert as which cluster is not in compliance for the license and you can add additional licenses as needed. If you remove a cluster from ELM and at next sync those licenses will be freed and is available. For example in a disaster recovery scenario, if one data center is down, I can bring-up another cluster in another data center, add my new cluster to the ELM. Remove the old CUCM cluster, do a sync on ELM, the licenses will be automatically consumed/allocated to the new cluster.
