pkh's startement about the SCL above refers to installing RALUS on the Xenserver host itself as it is in the RALUS section of the Admin guide, as the OP appears to be talking about protecting Windows VM's running in Xenserver, I don't think this section of the SCL applies.
This makes the issue more likely to be that when the remote agent for windows accesses VSS inside the VM, then the Xenserver Tools have some kind of function that detects this and tries to create a snapshot of the VM itself. As we don't have a speific Xenserver Agent (like we do for VMWare or Hyper-V) it is unlikely we are sending the correct requests to either start or stop the snapshot - so as mentioned earlier you may have to play about with any options for customizing any Xenserver tools installation to see if you can get it to not do this.
Just for completeness theVMware agent actually starts the snapshot from outside the VM and then calls in though VMware tools from this process to do the VSS request into the VM - which means the VMware process is fundamentally working in the opposite direction to what appears to be happening in this thread. i.e. VMWare Host starts snapshot and calls in through VMware Tools to request VM VSS operation vs RAWS starts VSS operation inside of VM, but then something in the Xen Tools calls the Xenserver host to request a VM snapshot.
