When 'df' tries to stat a remote (NFS mounted) filesystem whose root has permission for "other" of only execute it reports "permission denied" instead of displaying disk usage information. This does not happen with systems running earlier versions than RHL 6.1 (or another OS).
What OS/version is the NFS server software?
(SunOS 5.6 was the reply)
This looks more like a NFS client problem
The NFS client is limited to using the permission of the user executing the command. This cannot be fixed.