Are there any "traps" in cloning a VirtualBox VM for concurrent use on the same Host/LAN?

If you properly clone the VM using the vboxmanage clonehd commands it will create the cloned VM with a new mac address as well.

I am not sure with VirtualBox, but with VMWare there are no such problems. Multiple VMs can share a vmnic, and cloned guests get a new MAC address and what not.

My guess would be that you are fine (I do it all the time on VMWare workstation) and from what I have seen of VirtualBox it is very mature. Try it out, if it doesn't work, then worry about it.

Watch out. With VirtualBox, cloned VMs will have the same mac address as the original one. Therefore, the network will not be able to differentiate between the two. Currently, you will have to manually change the mac address of the newly cloned instance BEFORE starting it to avoid conflict on the network.