useradd and userdel have a -R option to run in some other chroot too. You could try creating a test user on the / partition, and delete it later if required? It wouldn't be a case of looking at the logs to see where it hangs if it isn't consistent, but search them for "error" and "warning". You should have collected something on some boots that will now be saved in /var/log.
# /usr/bin/useradd --create-home --groups wheel,rfkill,network,audio,optical,floppy,power testuser
# passwd testuser
New password:
Retype new password:
passwd: password updated successfully
# userdel -r testuser