View Current Group Memberships - checks to see if this group part of any other group (parent group). This does NOT have to do with whether group is referenced by ACL or workflow.
You can query against ACL definition to see if the group is referenced:
select * from dm_acl where any r_accessor_name='group_name'
As for workflow, you can query against activity performer to check for the same thing:
select * from dm_activity where any performer_name='group_name'
If you have a specific group you want to reassign to, there is reassign method in Documentum Administrator that can do this for you.