Okay. So when using a VLAN backed pool, you associate the entire pool to a Distributed Switch.
When an isolated network (Org Network, in your case) is created, vCloud will create a corresponding port group on the Distributed Switch.
What you need to ensure, is that all VLANs are trunked to the ESXi NIC Cards assigned as uplinks to this distributed Switch.
For VLAN backed Network Pools, there is no additional MTU requirements.