I spoke with a ranger at the Kelso visitor's center, and she said not only closed, but one could get cited if found within the boundaries of the park. What??? (So I climbed Mitchell instead). However, she said there was talk about opening the park on a limited basis this fall some time.
I drove by the visitor center around 5:30 pm on May 22, 2016. There was a ranger's police cruiser at the building and one hiker car parked in the lot. It looks open. The Hole In the Wall campground was also open with some campers in RVs.