Gluu can use any LDAP server as backend. LDAP protocol is an industry standard, so anything that adhere to it will do. But Gluu Server doesn't support any AD's proprietary interfaces, so there is no full integration into AD environment. It just can pull users from AD and verify their credentials (with LDAP bind), that's it.
Regarding the original issue, just an idea: are you sure you use AD for authentication in Gluu? Basically, you need to configure two things in Gluu: Cache Refresh to pull in users from AD, and add your AD server at Manage Authentication page in web UI so it could be used for authentication as well.
Is that what you do? Could you provide screenshots of your CR and Manage Authentication UI pages with all settings visible?