[thejeff]

I find it difficult to imagine that PBEM works differently than network in this situation. And Wraithlord just tested the 2 nations from the same machine & key in network, so it's OK there.

I've seen reports of CD key violations and it's become common wisdom that you can't play 2 nations, but I don't recall a report that actually stated they played both nations from the same machine and had a problem.
Using the server to set a nation AI can cause it, if you're playing your nation on a different machine.
I'm pretty sure it's been the same since Dom2.

llamabeast, would you be willing to set up a game to test this and figure out exactly what does happen?
Should be as simple as starting a game and having someone submit 2 turns from the same machine & key.
How is that different from the server's perspective than a hotseat game? Only that the server is different machine, right?