I am not sure about the scenario you are pitching but nested Organizations aren't supported in vCD (neither via APIs or UI).
Sure Organizations can "share the same resources" in the sense that a Provider vDC can be used to back more than one Organization but it's not like you can create OrgA and WITHING OrgA you can create OrgB and OrgC.
Massimo.
Massimo Re Ferre'
VMware vCloud Architect
twitter.com/mreferre
www.it20.info