Trond Myklebust of Network Appliance, who is also a developer of the Linux Kernel NFS client, told me that the new Linux NFS client behavior is intentional and supported.
Starting with the 2.6.18 Linux kernel, Netapp snapshots have a different device number than the corresponding live volume when viewed with NFS.
The change was made to better support NFS 4, which allows a NFS client to cross mount points on the NFS server provided that the server has exported everything appropriately.
So just to confirm, this change in behavior does not require that NFS 4 is actually in use? We'll still see it in a v3 mount as well?