Good question! I think many others would ask the same. IIUC Both Samba and Microsoft say a public DNS name is preferred:
From Microsoft site:
Using single label names or unregistered suffixes, such as .local, is not recommended.
From Samba site
The domain name should still be a valid domain name
https://wiki.samba.org/index.php/Active_Directory_Naming_FAQ#So_what_should_I_name_my_domain
no more .local 
Please note also that the acronym “pdc” (old NT Primary Domain Controller) does not apply to the Active Directory world.
Moreover, the Domain Controller is not the NethServer itself, but a container, something like a virtual machine, that is assigned the IP address you specify on the “Start DC” web page.