Hi Claudio,
I hope you're well and wishes you a great 2016 year !
I don't know anything about Zentyal but I have already used the standard LDAP module with Dolibarr and Active directory.
Once setup, you can create a new user by retrieving datas from the LDAP. You can also use sync script to have users and groups synced with the LDAP.
Beware, you must have a login/pass in the LDAP that has rights to read users and groups, this is this access that the module will use to communicate with LDAP.
Then you have to add specific LDAP informations in the conf.php file (same as in the module setup).
Cheers !