There are definitely scams that certain ethnic groups are involved in (Indian tailor scams? Chinese tea/art scams?), but this has more to do with skill diffusion more than ethnicity; people willing to scam learn it from someone close to them, and it seems 419 scams have achieved critical mass in Nigeria so the diffusion is pretty broad now (couple with an economic situation that makes scamming somewhat desirable).

I've met plenty of Nigerians who are not scammers. Stereotypes melt away quickly when you meet real people, but the survival filters remain in place.