I'm not sure why you need to add vCD users to EM. Authentication of vCD users is done in realtime by checking credentials and permissions against vCloud itself, there's no need to create those users in EM, that's the whole point of having native integration. You just open the dedicated url for a given tenant in EM and login with a org admin.
EMEA Cloud Architect @ Veeam Software
Veeam VMCE #1