osTicket does not have an LDAP account name. osTicket does not talk to LDAP.
You can install the Authentication::LDAP and Active Directory plugin which lets your users authenticate with LDAP/AD. But it does not add a LDAP Accountname to the software. It also will not update a password to LDAP/AD [Which is considered dangerous].
You are correct that the username is in the ost_user_account table. To get the information query the table for the username of the user id.