I think "Users and Groups" is supposed to not show system users and groups to not confuse users (the GNOME spirit !).
So I suppose that under Debian/Ubuntu, it should rather only show GID >= 1000.
Basic system groups seems to be "exposed" via the privilege tabs, hence maybe a fix to bug #133862 would be to add a "Raw access to disk" privilege linked to the disk group.
I think "Users and Groups" is supposed to not show system users and groups to not confuse users (the GNOME spirit !).
So I suppose that under Debian/Ubuntu, it should rather only show GID >= 1000.
Basic system groups seems to be "exposed" via the privilege tabs, hence maybe a fix to bug #133862 would be to add a "Raw access to disk" privilege linked to the disk group.