In case someone rebuilds this for RH6[01], they have to make sure they've installed the errata pam package; pam_stack used in pam config now was added between 0.68 and 0.72. This might be a little redundant, but adding it wouldn't hurt I think.
The -servers package already has a dependency on /etc/pam.d/system-auth, which is also only provided in newer PAM packages. That should be sufficient.