I don't know of any privacy policy on it but HN doesn't really overlap with YC applications. pg used to say that he'd sometimes recognize a username as being a smart commenter on HN, and maybe that would be more likely to get them an interview (I suspect as much because he wanted to meet the commenter as because he thought they might be worth funding). But I don't think it was ever a big deal, and I doubt happens at all anymore. "An important source of unadulterated intel" is definitely not true.

Sometimes I notice someone doing interesting work on HN and get in touch with them and try to convince them to apply to YC. I'd like to do more of that.