Better late than never! This is a very well-considered response, though I regret to say that I haven't been keeping an eye on news on this issue.

As for the Nigerians in Ho Chi Minh City, I don't know closely the dynamic resembles that of the Romani/France situation. I've only been to France once for a short stay and never encountered anyone who identified themselves as Romani, so I can't really draw a parallel personally. The "Nigerian Prince" thing isn't well known in Viet Nam though, but that's likely due to a number of factors, including that Western Union can only be used to send money into the country, not out of it and that credit cards were only introduced in 2009 or so. In Viet Nam, it's the Chinese who are known for e-mail scams and credit card/banking fraud.

From what I understand, Nigerians first started going to Viet Nam after the country re-opened in 1991, in the interest of working in the oil industry and then found that there were other opportunities to make money there, especially given the lax security. Many of the foreigners in Viet Nam come from a more blue-collar background, because the need for foreign expertise is much higher in industries like oil and engineering related to shipping, than for corporate types. That might begin to change soon, but who can really say?

I wish I could point you to a scholarly source rather than my anecdotes, but I don't think it's been a subject of academic or journalistic interest of yet (or at least, not much interest). I don't know where you're located, but Viet Nam is an increasingly accessible country and very safe as far as SE Asia goes (maybe Laos is safer), plus it's very affordable once you're actually in the country, though getting there can be a pain in the ass.