The LDAP plugins do not really sync users. It allows auth for an existing usr to be LDAP.
There is the core Authentication::LDAP and AD plugin from osticket.com/download
If you want to Sync your users so you do not have to create them then there is a paid adSync plugin from software-mods. But you still need to have the LDAP plugin for them to authenticate against AD/LDAP. It autopmates the process of creating your users for you.
If you need to have multiple different domains authing against LDAP/AD then you would need to get this one that you are talking about working.