You can mimic the NAT'd functionality from Lab Manager by creating a vApp Internal Network and then connecting it to your External network within the Organization. If you have an IP Pool configured for this network and choose this selection on your VM's within your vApp it'll function just like Lab Manager did.
When you create this connection to the external network within your vApp you decide if you want it NAT'd and/or Firewall'd. You can also check a box at the far right to force it to keep the IP addresses from the external network IP Pool.
The drawback to this is if the config is cloned the IP addresses go with it. You will only be able to start one vApp at a time unless you change the networking on the cloned vApp. We do this for some long-term testing/development vApps where we have to create other network ACL's in order to connect to it.
Eric