Eh, I disagree with your definition of "white hat SEO".
White hat is about earning links. A arms length third party has to give you a link for it to count.
That means it has a lot more to do with Public Relations than Page Rank.
If you drop a link yourself in a forum or blog comment, that's fundamentally NOT white hat. That's just non-automated black hat. That's also been below Google's radar.
This is the fundamental problem with SEO... People like you and me who are arguably 'experts' disagree about these definitions.
Ignorant clients hear "forums links are white hat" and reasonably extrapolate that "automated forum links are just scalable white hat SEO." And then they get into trouble.
I've seen it happen at some very well-funded startups. The marketing team looks like geniuses... for a while. Until they get nailed, then they claim they were tricked by a black hat SEO firm.