There are a couple of things that need to be done.
First, usually, you will need to Extend eDirectory with the RFC 2307 Schema. See:
http://www.novell.com/documentation/edir88/edir88/?page=/documentation/edir88/edir88/data/amijij0.htmlThen you will need to configure your RedHat to use LDAP for authentication.
There is a pretty good article on this here:
http://www.novell.com/coolsolutions/feature/5811.html-jim