Some YC companies definitely do. I'd guess that most startups do to an extent.

I think if anything frequent use of HN would reflect poorly on one's productivity.

The same could be said for someone who says "I read books all the time." You could look at it as someone being unproductive (hey if you're reading a book, you're probably not working!) or you could look at it as someone educating themselves.

I've learned a great deal by reading Hacker News.