The Active Directory Agent is used to perform granular backup and restore of Active Directory data, and to do restores without having to perform an authoritative restore.
Without the agent, Active Directory will still be backed up as part of system state.
I think it's normal for nothing to show up in your restore selection as a subcomponent of Active Directory (without using the agent and GRT). As long as the Active Directory itself shows, it should be OK.
Of course, the best way to find out is to do a DR test.