Have you looked at "Advanced Cross vCenter vMotion"?  This is included with vCenter 7.0U1c and may make your life easier - Introducing the Advanced Cross vCenter Server vMotion Capability | VMware.  

Hi,

same migration one year ago:

1. Mount the Nutanix datastore to the new Vxrail cluster.(you can expose the Nutanix datastore in NFS)
2. Shutdown the Vm's in Nutanix , registered in the new cluster and poweron on Vxrail.
3. Storage vmotion from Nutanix datastore to the new Vxrail datastore.
4. Unmount the Nutanix datastore

There are minimal downtime of the VM, only a shutdown-poweron, but far better then Veeam!