I'm used to joining windows 2008 r2 AD with Krb5.conf/ldap.conf/smb.conf and pam.d/authconfig_ac and being able to list users with getent passwd but after joining a centos 7 system I can logon fine, but I can't see users in AD who are able to logon. What do I need to look at to fix this? I'm just getting my feet wet on Centos 7 and used the join realm to join the domain.
There has to be a trust relationship between AD and your Centos server. I would start there, check if AD is actually allowing you to make that query from the Centos server.
/var/lib/sss/gpo_cache and check that you have GPO's being cached. Match the ID's to current GPO's and you'll start to see who is allowed.
Note that SSH access is controlled by Terminal Services GPO.