I don't think urbackup supports hyperv vss for backing up VMs without downtime. You will need to back up VMs from inside them, as if they are a physical server.
So if you want to back up VMs at the host level, which is a major benefit of virtualization, then you are stuck using a non open source backup solution. If you want free, then you will just have to use the built in Windows Server Backup or hope you are within the limits of the free stuff like Unitrends.
If you have the time to figure out how to get AMANDA to use hyperv vss for example, do share!
Right, it's simple agent only.