I have a vmware esxi 6.0.0 running, it is licensed as below, and I have Veaam free edition. A manual backup to a NAS device fails with "Processing Windows8.1 x64 OB Error: Current license or ESXi version prohibits execution of the requested operation." It isn't a permission issue as there is a 30MB file created on the NAS.
Product: VMware vSphere 6 Hypervisor Licensed for 1 physical CPUs (unlimited cores per CPU)
I get the same result if the guest is running or not.