Joining on NS7 still works?
Did you go through the post migration steps for samba in NethServer 7 migration — NS8 documentation?
Yes, you can use dnsmasq for DHCP but not for DNS when port 53 is used by samba, see also NethServer project milestone 8.3
In NS7 the samba DC had another IP, in NS8 usually the host IP is used to be reachable from clients.
To get the IP, you could use
ip a