One method is to use the 'canonicalName' to designate the OU. The condition can be used in a 'If-Else' Branch as 'canonicalName of Parent OU of Workflow Target'.
Also works if there are multiple OUs named the same name but at different locations in Active Directory. An example might be the following two 'Users' OUs. "Testco.local/Regions/North America/Users" and "Testco.local/Regions/South America/Users".