Stacki doesn't have account sync natively though we have seen some ways of handling it.
In the previous enterprise version, we used Salt to sync user configuration but that was assuming Unix uid/gid served from the frontend.
We have had a few clients in the past who have used LDAP/AD authentication by using sssd on frontend and backends. I have old config files lying around. But those deployments assumed backends could get to the LDAP/AD servers.
It was a hard solution to test because we never had LDAP/AD systems internally to figure it out for enterprise solutions.
In most deployments we've seen, rarely are users allowed on backends, but if you're serving files and accounts from NFS or other network storage, I can see why you may need them everywhere.
Ansible might be a good fit here also.
Thanks,
Joe