There's still a risk. Assuming you have done a good job of keeping your personal information away from "JohnnyFlash", no one will find your company through your posts here.

However, what about the other direction? Suppose your company comes to their attention through some other means, and they start investigating. At some point, you could find yourself answering questions under oath. It's conceivable the questioner might go on a fishing expedition, and ask "Have you ever posted on HN under the alias Johnny Flash?" (he might ask that at every company he investigates).

Then you've got the annoying choice between telling the truth and making your company's case for accidental violation much worse, or lying under oath which, if that is discovered, could bring serious penalties.