1. Utilize the adopt a vCenter/VM function that's been around since 8.20 days. Works great and you can drag/drop into the oVDC RP assuming networking is in place. https://www.paluszek.com/wp/2018/10/23/migrate-vms-and-networking-to-vcloud-director-video-walkthrough/
2. Utilize vCloud Availability for Cloud-to-Cloud or 3.0 (when it's GA here shortly). Provides self-service migration, but does require some minimal downtime (power off and power on). Can be done via the tenant or provider.
-Daniel