Is it OK to mention it when it appears that a poster is spamming paywalled content for a specific site? For example, this guy [1] stopped posting altogether almost immediately after I politely pointed out the sheer volume of paywalled WSJ articles he was posting [2]. It isn't inconceivable that this account (and many others) were created solely to spam paywalled content to HN. If we are forbidden from mentioning such things, I think we are going to have a problem around here with many more attempts by paywalled sites to exploit HN.
Sure, that's such a special case that I don't see why it would be a problem. You can also email us (hn@ycombinator.com) when an account is using HN solely to promote a particular site. If we can email them, we often ask people not to do that. And in egregious cases we take away submission privileges.
People out to promote one specific site can happen regardless of if the site has a paywall. Someone could always promote one specific ad supported site as well.
[1] https://news.ycombinator.com/submitted?id=abetaha
[2] https://news.ycombinator.com/item?id=9641922