Yes, RedWeek is legit. Many members from Timeshare Users Group (TUG) list their rentals there. Some pay to use the Verified and Protected listings, others who are just as trustworthy don’t.
However, when it comes to D.V.C. rentals, stay away from any that state there’s a $190 fee to pay when you check in. Those are exchanges made via Interval International and are not allowed to be rented, and if either II or D.V.C. find out, they can cancel the reservation.