If all you are trying to do is link physical servers on switch ports to VMs running inside vCD then you don't need to deploy Edge's (or have any routing at all).
You can make VLAN-backed vCenter portgroups available to tenants in vCD via External Networks provisioned in 'Direct' mode to Org VDC networks and everything happily co-exists in the same Layer-2 network.
If you need a different vCD network (e.g. a different Layer 3 network) then you can of course use an Edge gateway to route between networks, you can also deploy an Edge as a bridge linking a VXLAN and VLAN as a single Layer-2 network, but I don't think you need to go this far from what you've described.
