I dont know. I think the point of "santa" is that, well, it looks like Santa. That's why people stuff their bellies and wear a beard. And santa is definitely male and caucasion, according to tradition. So there's definitely a stock "something" to expect.
If there's a female/not caucasion person, it kinda makes you think "person dressed up as Santa" more than someone who's male, with a real white beard and caucasion. It's the whole suspension of belief thing - it's a lot easier to do when the other side helps you along, kwim?
That said, in Vegas, there's tons of impersonators that arent "typical" for whomever they're impersonating and still do a great job at it.