I wonder if a Windows Domain DNS Server should register any Domain Member in general? I notice that this does not happen if the DHCP is an external system and not aware of the internal DNS Server.
Windows AD DNS usually is updated with all your domain member and network host IP addresses for both - the forward and the reverse lookup zone. There are two mechanisms for updating
In the latter case the DHCP client service (yes, confusing, but this is just how it is implemented) is responsible for sending the DNS dynamic update. The behavior is configurable via group policy settings.
A lot of things automatically register themselves in an Active Directory environment.
Nearly all of them do it through Dynamic DNS Update.
The problem with "external" DHCP servers is generally not that they don't attempt the registration. Several are capable of this. It's that they speak the wrong protocol for secure Dynamic DNS Update.
How long did you think about it?
here is an angle you have mised: How would DNS know all members? Especially of those are not active or moving. Ups - does not work. Simple. DNS never will know all systems around / existing and their IP addresses.
Yes. Because this is a function of the internal DNS server and it is in general a BAD BAD BAD idea to use an external DNS, exactly for reasons like that. Plus the fact that dynamic DNS updates are something that... are not really used that much outside the MS world.