That's correct; currently only the "OTHER" group is supported.  This group includes all UIDs in your subtenant.
Dear,  I can use the x-emc-useracl to set the access rights to an object for the specified UID(s).  Now, I want to share the user files to the Group. I find the x-emc-groupacl. It can sets the access rights to this object for the specified user group(s), but Only the OTHER group is supported. How can I share the user files to specific Group? Does this group equal to Subtenant?  Thanks.
Sharing files to the Group in ATMOS