Let me expand on what I said earlier:
I don't think surnames are a very reliable source for pinpointing a specific heritage, or there at least need other factors than just a name.
Look at the surname Martin. It's roots come from English, French, and German descent, but there's really no telling what Christy/Wade's heritage is. And yes, Pedro certainly does have a Hispanic name, but he doesn't look or sound it which makes me just think Rockstar just changed his name late in the game or something.
Now, Justin's last name is Vandervelde, and I'm pretty sure Van der Velde is of Dutch ancestry. However, I actually think that Justin is Greek based on his "pleasingly Grecian" line he says when looking in the mirror and how he bitches there should be more Greek marble sculptures around the school. Or he could simply like the culture. Who knows.
That said, I have a problem with the preps in general. Spencer is the only surname out of the preppies that has a singularly English background, but Tad admits his faux-British pretensions. Gord also fakes his accent (as he occasionally slips in and out of everybody in town wait what it) while some others don't have one at all. I dunno, it just makes me wonder if some preps are faking their ethnicity as a whole.
Now that's not to say they aren't English/what have you, but to me there's really nothing about them that screams they're from that background.
