I'm not certain the hack redhat added to force openldap to use nss actually causes openldap to use the nss cert store. My rhel6 openldap servers appear to just use the PEM certs they would have used as if redhat never messed with forcing openldap to use nss, but rather left it at openssl. I did check and slapd is linked against the nss libs, but using the pem file in /etc/openldap/cacerts.

The  fix for this might be as simple as linking the PEM version of the updated cert store into the directory where openldap is looking.