The article does not even hint at the Common Ground series of conferences, based at the School of Education at University of Illinois-Urbana/Champaign, which specializes in high fees, abstentia fees, and apparent pay-for-publication, across a range of discipines. When will we see some reporting on Common Ground?
You probably won't credit what I say here since this is a first time post, but here goes. I've been lurking sporadically on this forum for a few years, for what that's worth.
Although I cannot speak to the legitimacy (or lack thereof) of Common Ground as an organization--and what do we mean by "legitimate" anyway?--my sole experience with one of their conferences was wholly positive. The atmosphere was lively and intimate, and the conference brought together a very international group of scholars with similar interests who were eager to engage each other. Anyway, it was recommended to me by somebody I trust, so I did not approach it suspiciously.
As for their journals, they are probably closer to double-blind refereed conference proceedings in practice. There was a lot of talk from the organizers about wanting to upend hierarchical (non-meritocratic) and big corporate structures of traditional academic journal publishing--and of course they have valid criticisms there. Common Ground seems very ambitious when it comes to new academic publishing models, though I would question how much impact they are ever going to have.
The conference was good for bringing people with interests in common together to exchange ideas and build community between the attendees. Inasmuch as that effect matches the organization name, and this is what conferences of all sorts are for, generally speaking, it was "legitimate." Beyond that, I guess everyone's mileage will vary.