A new KB was published yesterday to provide guidance on using Veeam Agents to backup VM's hosted by XenServer and XCP-NG environments managed by Xen Orchestra. It's not direct VM-Level backups, but since I know people have been requesting XenServer and XCP-NG support (especially in Reddit it seems), it's a step in the right direction. This was previously posted a couple months ago (link below) but I wanted to share the official KB.
This article documents how to use Veeam Agent for Microsoft Windows and Veeam Agent for Linux, managed by Veeam Backup & Replication, to protect virtual machines in XenServer and XCP-NG environments that are managed by Xen Orchestra. While these hypervisors are not directly supported for VM-level interaction by Veeam Backup & Replication, this article demonstrates how protection is possible through guest OS-level backup agents.