The behavior on whether or not rhncfg-client diff will display the differences in a readable-by-root-only file can now be controlled through the -d or --diff-secure-files command-line option or through the display_diff option in /etc/sysconfig/rhn/rhncfg-client.conf.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHBA-2012-1552.html