Adding a XenServer cluster with existing VMs

[David Ortiz]

Hello,
      If I have a XenServer cluster with VMs that already exist and I add it to 
Cloudstack, what happens?  I saw in the documentation that it should not have 
VMs running, but does this mean they should not exist or they should be 
stopped?  If the former, will the Cloudstack addition fail, will the VMs be 
deleted, or will they exist in a seedy shadow vm world where xenserver manages 
them but cloudstack does not?
Thanks,      Dave