I tried it and the policy is applied. With strong policy the password needs a special character. I tried to create a new user in ADUC and it was not possible with strong policy and without special character.
Without strong policy you still need 7 chars AFAIK.
For changing user passwords you may login to Nethserver web UI too.
For advanced settings you may go to command line:
systemd-run -M nsdc -t /bin/bash -c "samba-tool domain passwordsettings set --help"