I'm not sure I see anything illegal in there (from the perspective of PA employment law anyway). His biggest beef seems to be that they mined data without their employee's consent, but most of the places I work explicitly state that emails, chats, electronic and physical documentation (work products) all belong to the organization.

On one hand, this feels a bit scummy - on the other hand, I'd rather work somewhere that's not toxic. I think the biggest issue is that I doubt their technique is good enough to a) find all the toxic people (one of the most toxic people I ever met was outstanding at never putting it in writing) and b) will exclude people that could have improved the company.