The posts are explicitly differentiated from normal submissions - you can't comment and they usually say something like "X (YC year) is hiring". That's not a dark pattern. I agree that some people may not understand what or why these posts are and not look into it (answers are easily available) - but that doesn't make this a dark pattern.

Hackernews has minimal ads, lax account requirements, professional moderation, minimal intrusion from owners - and you are hyperventilating about 1 post in a 100 being a marked ad?