I actually did this a little while ago and forgot to post about it. I could not get NFS to work between XenServer and Unraid. So, I scrounged up some hardware and punted. I installed OpenFiler and iSCSI.
And it worked.
Angels sang. Rainbows shone. Something about unicorns...
It's been working great. I just have a new problem. The hardware I've been using for XenServer is my old PC hardware. It's 1st gen i5 so it should be plenty for my limited requirements, and it is. It's just getting hung randomly now. I had this problem when it was my PC. In fact, that's why I upgraded. Looks like it's hardware related. So, now I'm contemplating getting a new MoBo and CPU. What a drag.
The good news is, I'm pretty sure I'll be able to go to all XenServer and get rid of the VMWare, all while retaining live migration across the iSCSI pool. VMWare, I'd love to stick with you, but I need live migration in the free version.
Being on a XenServer has another benefit. I might try something like Puppet, just for kicks. :)