Hi Thorsten, The issue I reported that prevented systemd-sysusers from being used without systemd as the init system has just been fixed (#926316). So in theory we should be able to use it with other init systems. But the fact that elogind conflicts with systemd creates another hurdle.
If the conflict can't be lifted I can see two solutions, either elogind provides its own version of systemd-sysusers, or systemd-sysusers is extracted into an independent package that doesn't conflict with elogind (I've filed #946456 for that). Emmanuel Bourg