The change log for Version 3.40 (2 May 2007) lists this point:
Added Module Config options for external quota commands to use, instead of the standard Unix commands. This allows a different quota system (such as ZFS or on an NFS server) to be used instead.
I'm very interested in making ZFS quota (file system quota and user/group quota for zfs) configurable via webmin/virtualmin:
Currently we create a zfs file system for each virtual server and set the quota and reservation properties. Could you please explain how to do that via webmin? I don't know how to replace the commands like
repquota -v edquota quotaon
etc with ZFS equivalents?