Here is what you can do: (this solution works only if you can do VMotion between old and new set of servers)
- Configure iSCSI(assuming you are configuring SWiSCSI) on new set of servers.Make sure you create you vSwitch for this.
- Configure VMotion on new set of servers and check if configuration is fine.
- Do Enhanced vMotion of VM's from old set of servers(where source datastore is NFS datastore in your case) to new set of servers(select the destination hosts from new set of servers pool and destination datastore as iSCSI datastore)
- Then remove new set of servers from VC after done with migrating all VM's to iSCSI datastore and add them to your new vCenter server.
If you cannot perform Enhanved vMotion on your setup:
- Configure NFS(as on old set of servers) on new set of servers.
- Configure vMotion on new set of servers and make sure there is no configuration issue.
- Migrate all your VM's to new set of servers.
- Then do a storage vmotion tose VM's to iSCSI datastore.
- Remove new set of hosts from VC and add them back to new vCenter server.