Thank you for testing!
This use case is not still covered. 
I know there are some users that require such configuration, but from our metrics this is a feature rarely used.
For the moment, we focused on the most-common use case: AD DC and file server on the same machine.
Otherwise, you could create the AD DC on NethServer and join a NAS to it.
Maybe we are going to add your use case, but I think that will not happen for the first stable. 