A UUID mismatch between two datastores occurs because the UUID is based on a hash of the NFS Server and Path, as seen by running esxcfg-nas. If you have specified the NFS server information using different methods on different hosts, then the hash value, and ultimately the UUIDs will be different. — VMware KB 100590
But what if I can't?
In ESXi, open SSH or the DCUI and login as root, and then edit the hosts file by adding an entry: point host 1 to IP 1 with its NetBios or DNS name, and point the second host to a different IP (since they are physically separate ports) but use the same name. This way you can add the NFS datastore by name, and the UUID will be consistent across the servers.