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.
Years ago I recall listing your hacker news user name was part of the YC application process (I have not applied in some time). Hard to believe that it wasn’t used as a screening mechanism at some point in the application process. Humbly defer to you of course.
YC and HN use the same account system, so you still apply with your HN username. But it's not used as a screening mechanism and, as far as I know, no one involved in YC applications is in the habit of looking at HN posts. Certainly not systematically.
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.