Are Group Families supported in Managed Units?
Group Families are not supported in Managed Units because Managed Units are simply "search results" - they are not actual containers that you can create objects in. Group Family rules are designed to create subgroups for the Group Families and because Managed Units are simply read-only search result objects, the Group Family groups cannot be created.
This is by design. Group Families must be created in Active Directory Organizational Units (OUs).