I've tested this quite a bit now, and it works fine for moving managed machines between reservations for the same Business Group.
However, although the workflow will complete when you select a Reservation that maps to a Business Group that the VM is not currently associated with, you will end up with the Deployment object (and potentially other references) still registered in the vRA postgres DB under the original Business Group. This then causes issues if you later try and run a "Bulk Import" to migrate the VM/deployment to a different reservation and/or Business Group (it will fail for that server).
This workflow that used to work well for vCAC 6.x also results in the same issue described above in vRA 7:
http://www.wolowicz.info/2015/07/moving-vms-between-vra-business-groups-and-reservations-in-vco/
The only way I've found to reliably move managed machines between reservations associated with different Business Groups (i.e. move a machine to a different Business Group) is using the Bulk Import functionality which is painful.
Grant / VMware - where is this functionality in vRA 7!?
We need VMware Engineering or the vRO team to provide a workflow (and demonstrate the correct API calls) to do this ....(please please)