The doc will guide you trough websites you can use to adapt AIX to use LDAP authentication.
This info is valid for AIX 4.3.3, AIX 5.1, AIX 5.2 and AIX 5.3.

mksecldap command
LDAP Authentication Load Module

Make sure that if you use AIX systems <5.2, you'll need to setup an AIX schema. This also means that systems <5.2 cannot auth. against an OpenLDAP server doing auth. for multiple platforms, you'll need the AIX schema in the OpenLDAP server.
RFC2307 is implemented from AIX5.2 onwards.