I have not as the elk in my hunting area are just not predictable enough that they travel in a defined area with regularity. I always find myself chasing them, rather than them coming to me. Also, too many wallows and water sources to make them worthwhile and predictable to hunt over.
What state and how dry was it that your friend found success with a blind over wallows? I can check 4 wallows within about 1000 yards of each other in the area that I hunt, so it would be really hard to figure out which one is the "honey hole".
Southern Nevada. Really dry area. He has a "honey hole" that has 2 watering holes about 1/4 mile apart. He had game cameras that showed a big bull visited both regularly but he just couldn't pick the right one. He finally got lucky on a nice bull. Area 23 if you know NV.
This year i set up a ground blind for my fifteen year old who loves to chase elk, but gets tired about two weeks into the season. we have tree stands but he hates so sit in them. i set the ground blind on a hog back ridge where elk move from feed to water.it worked well . he was able to skoot a cow. when the elk came by the blind they never spooked and my boy was able to move around quite a bit to get ready for the shoot.
There are some guys that use a blind where I hunt on public land, at a seep about 3/4 of the way to the top of the mountain. They have scored several bulls at that seep. I think they have actually camped overnight in the blind. It's a good hike to it.
I would suspect that making cow calls and having a decoy at the seep or wallow would be a great help. I could not sit in one for long. I love the "hunt" more than the "wait".