Backup of OpenBSD under VMware

Hello,

the scenario is a cluster of ESXi nodes on which OpenBSD should run as a VM.

Currently the cluster is being backed up by Veeam, I tried to insert th
obsd VM inside the backup job but no success, with following "Error: An
error occurred while saving the snapshot: Failed to quiesce the virtual
machine.". This looks strange to me because the open-vm-tools implemented
inside the kernel are usually functional to ESXi hosts.

Questions:
1. has anybody found a way to use Veeam to backup OpenBSD VMs?
2. are there any other suggested softwares to perform a similar task?

Thanks