There is a new LDAP search function available in UCM 11.5. In the previous version, you can only search against UDS, the UCM user database. Although with LDAP integration that means you can still search the LDAP users after they are imported to UCM, it will return the local UCM users as well. In this release it is allowed for the endpoint to search against the LDAP through UCM.
In my lab the DXs are working fine. However the 8861 corporate directory is still searching against UDS. Still finding out the reason, will update this post once I know why is that.