I think I discovered this a long time ago but forgot until the other day, however I still didnt see any non warlock or program wall hacks when i searched. If you have the obsidian nightwing mount you are able to walk through INVISIBLE walls in SoO. This probably works for all other invisible walls but I have not tested it.
People can also jump on your back and walk through the walls as well BUT they will be stuck on the other side unless they mount you again to return. I got this on video when I was raiding last week but I will only post a couple screens from the video since I do not feel like finding an editor to remove the names.
I dont know why you would want to do this other than to maybe skip shamans if you cant kill them. It probably works for all other invisible walls but i dont have time to test it and + the no theories here yadda yadda so i'm just going to leave it as; the obsidian nightwing mount ignores the invisible wall between shamans and nazgrim, obviously not intended since no other mount or non hacking program can get you through the wall.