Yes, I  have "camped" at Wal-Marts all across the lower 48 and Alaska and some in Canada. We have never been questioned or asked to move. A very few are posted "No Overnight Parking" so we just move on when we see that.
     The Wal-Mart in Whitehose, Yukon, Canada must have had at least 300 campers there when we stopped there this summer. It is the most scenic Wal-Mart I have seen as it overlooks the Yukon River.
    We usually arrive late and leave early when "camping" at Wal-Mart but I see RV's at our local Wal-Mart in Albuquerque all the time.
Doug