This module adds LDAP support to Open Atrium 2. Specifically, this ties LDAP groups into OA2 Spaces and Groups by adding fields to the Space and Group content type using the ldap_entry_reference field. Also provides support for using the Email Registration module to handle email-based authentication. All of the LDAP integration is actually done by the og_ldap_api module. Currently OA2 is using the LDAP module for the server plugin, although other plugins could be written (see the og_ldap_api project).
So, even though LDAP is part of the make file, it's not a strict dependency for OA2.