To clarify: are interesting blog posts that double as job ads still allowed? It's fairly common for companies to post good technical blog posts that are also meant as a "look at this fascinating stuff we're doing – you could be doing it too!"
Yes, those have always been ok. If a story is a good HN post in its own right, there's no problem. Sometimes people push the limit in weird ways and we have to decide which side of the line a post is on, but that's rare.
Rather than looking at the lowest common denominator, I'd hope that such blog posts are something that would have been worth writing and sharing even if the company was not in a position to hire. To put it another way, if a competitor wrote it and posted it, and it made the front page of HN, you'ld still be glad that they did despite it giving the competitor a leg up on attracting candidates.