Wolves look a lot like huskies, don't they? And I can't imagine any of the Alphas letting any vanilla mortal get close enough to their wolf forms to tell the difference.
Wolves are much, much bigger than huskies. On the low end of the bell curve, male gray wolves are about 70 pounds—a bit heavier than the biggest huskies. Wolves can grow to 180 pounds. They're a bit taller, and about eight-ten inches longer, which is significant. They also have heads that are a lot bigger in relation to body size.
In short, just from pictures, you can confuse a husky with a wolf, but if you see a big one in person, there's no mistaking them. And you'll also likely need a fresh pair of underwear.
Add to that Harry's insistence that the Alphas are bigger than natural wolves—not as big as the hexenwulfen, but still beyond what you'd find in nature—and I don't see how anyone could see an Alpha and not crap themselves. Also, I'm constantly disappointed that Mouse and the Alphas have still yet to really hang out.
As for the Alphas not being seen at all, well, I can only speculate that it's unlikely they haven't been spotted enough times to attract attention over the last ten or fifteen years. They've been involved in too many crime scenes for their pawprints, for instance, not to have been noticed.