The Release Notes of RHEL-5.0 mention that OpenLDAP is deprecated and will be replaced by Directory Server:
OpenLDAP Server and Red Hat Directory Server
Red Hat Directory Server is an LDAP-based server that centralizes enterprise and network data into an OS-independent, network-based registry. It is set to replace OpenLDAP server components, which will be deprecated after Red Hat Enterprise Linux 5. For more information about Red Hat Directory Server, refer to http://www.redhat.com/software/rha/directory/.
Red Hat Enterprise Linux 5.0
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