I'd like to put a few load balancing web servers out in front of my cPanel server, so all requests are directed to the front web servers instead of the cPanel server itself. I intend to mount the cPanel server's drive on the servers using NFS. Is there any way I can have these web servers use LDAP with the cPanel server so that the files on the NFS share show the proper owners?
cPanel LDAP Authentication will be available with the "Pluggable Authentication" feature. You can track the ETA for it here: http://forums.cpanel.net/f145/whm-pam-ldap-radius-authentication-pluggable-authentication-154665.html
CPanel does not support LDAP. You may be able to hack your way around this with some clever scripts, but it's not going to be native.
If you want to add it yourself, I'd suggest looking into CPanel's post-account creation scripts (or if you are using an external billing/control system, use that). You basically need to add an LDAP user once CPanel has created the user.