As clarification, when trying to import (into a vCD catalog) a nested vApp created in vCenterServer - vSphere Client under the vCloud cluster (and exported by File/Export/Export OVF Template...), I get the error: com.vmware.vcloud.api.rest.schema.ovf.VirtualSystemCollectionType cannot be cast to com.vmware.vcloud.api.rest.schema.ovf.VirtualSystemType . By "nested vApp" I mean: a vApp with children vApps.
vCD v. 5.1.0.816936
vSphere Client v. 5.1.0 build 786111
vCenter Server v. 5.1.0 build 799731