There are climbers in the photo on the left below. There is a guy in bright yellow that is not too far up.
We saw many people climbing the tower in various places. The first time we saw climbers we sat there for a while watching them. N2 also found places to climb around the back of the tower that was in the shade. Here are N2 at the base of devil's tower (there was no boulder field on this side so they climbed up one rock so they had climbed part of Devil's Tower!)
There were TONS of Japanese tourists at Devil's Tower when we were there. As N2 were getting their ranger badge (the ranger made them stand agains the wall so that it was better for pictures) there were several Japanese tourists taking pictures of them taking their junior ranger oath.