Should I contact accomplished researchers listed as editors of shady journal?
I wouldn't worry too much about tact.  There's enough information in your question to identify the journal, and it looks impressively bad, even by the dismal standards of junk journals.  It's so terrible that I'd consider it unethical to be actively involved as an editor, and humiliating to be passively involved.  Bringing this to the editors' attention would be doing them a favor: if their names are being used without their knowledge, then they'll find out, if they haven't been paying close enough attention, then they'll get a valuable wake-up call, and if they are already well aware of how terrible the journal is, then at least they'll learn that someone has noticed their involvement and disapproves.  Of course it would be quite an awkward e-mail.  Perhaps the easiest solution is an anonymous e-mail: it won't make things less painful for the editors, but at least it won't affect your relationship with them.