On XenServer 6.1 VMs with Windows 7 must use the new hardware version, 0002, otherwise the xentools will trigger a BSOD error 7B.
The VM can be verified with the command xe vm-param-list uuid=<your VMs uuid also used by vCAC as VirtualMachine.Admin.UUID>
When vCAC 5.2 creates new Xen VMs, you can include the custom parameter Xen.Platform.Viridian
Feature request: the code handling Xen.Platform.Viridian should be more generic so that all custom properties of the namespace Xen.Platform.* would configure attributes of the Xen VM's platform parameter.
What is urgently needed for Windows 7+ support is to be able to specify Xen.Platform.device_id=0002