NFS datastores should be mounted to the vSphere hosts, not guests unless you are creating a direct NFS guest mount. In the case of the former, you should be able to run SVMotion from one DS to another DS, both presented on you vHost Cluster.
If you have direct NFS to a vmGuest, you do not need SVMotion. Just VMotion your server, and make sure the destination vHost has the same sub-nets as your source. Unless I misunderstood what you are implying...