Probably a dumb question, but ..

I want to get a backup of our VM's, that is, the .raw file on the xen host.

Note that the VMs' user data is all stored on NSS volumes, which are mounted from a SAN, not part of the VM itself and already backed up through our backup solution, so all I'm interested in here is the OS, basically. Especially since these are OES servers tied into our Tree. They should be relatively static.

I know that to clone a VM, the VM must be downed first. Then the process only takes about 5 to 10 minutes or so. However, it is unlikely I'm going to be able to down our servers for even that long without protests.
Is there any reason I couldn't install my backup client on the host, and just backup the .raw files while the VMs are running?