The question I'd ask is whether they're up front about it. It's one thing to ask and see whether someone knows how to check if a number is odd or even - for that matter, it's one thing to use it as a programming quiz! Probably better than Fizzbuzz, everybody knows that one anyway. That's fine.
What would not be fine is to just quietly have that attitude and assume without checking that no one who uses Node a lot has any idea how to do basic things without relying on a library. It's not terribly uncommon for people to think that at least here on HN, I suppose, although I have yet to run into it in an interview or an engineering culture. But if your engineering culture is host to such attitudes, it's best for all involved to be open about that. You'll avoid wasting both candidates' time and your own.