Yup - would second that. We're a big Xen house here but also use VMware. A lot of shops appear to be using a 2 vendor strategy when it comes to virtualisation.
We are a two hypervisor shop (as are most hospitals). We use VMwareand XenServer. XenServer is used as we have XenApp servers hosting thousands of concurrent applications sessions. XenServer gives us one throat to choke for the Citrix solution. You are going to find a lot of people use something and Xen when they have a Citrix deployment.
Bumping this. Support for XenServer would be a huge value add for us. We are adding roughly 20-30 XenServers yearly right now and it is getting frustrating that we can't get the same insight into these hypervisors as Hyper-V and VmWare.