Can a customer have more than one edition in their environment?
No, only one edition (Standard, Enterprise or Enterprise Plus) can be used in the same physical location. Furthermore, all licensed editions must be the same across multiple locations to manage them through one Veeam Enterprise Manager.
This requirement applies to all Veeam Backup & Replication deployments, including multi-hypervisor environments. For example, if you have five licenses for vSphere and five licenses for Hyper-V in a given location, all ten licenses must be either Standard, Enterprise or Enterprise Plus.
Current customers who wish to upgrade to Enterprise or Enterprise Plus must upgrade all current licenses in order to receive a merged license file.