Any reason you are looking to go with Zerto over Commvault? We are waiting for Live Sync I/O so we can replicate the VMs but protect them at the same time. Zerto certainly has first mover advantage but I expect Commvault to do it better.
Not sure about replication using Zerto. I do know that if I backup a VMDK with Commvault and restore it to a completely different site and backup the newly restored VM it will show the jobs under the same client so I would assume the same license. That is also assuming that you are not backing up both VMs at the same time and a zerto replicated VM acts the same as a Commvault restored VMDK.
Also, I think you Zerto replicated VMs are going to be discoverable immediately after the first replication. So there needs to be a manual process to say hey back these up now.