The current 2.03 GA release of the ad_server probe is not certified to work with Active Directory 2016. The ad_server Release Notes -> Probe Specific Software Requirements section indicates that the probe is only certified for use with the following versions of Active Directory:
Windows 2008
Windows 2008 R2
Windows 2012
Windows 2012 R2
You would need to create an Enhancement Request by opening an idea on the UIM communities page to get Program Management to look into adding certification for the Windows 2016 Active Directory to a future release of the ad_server probe.