That wallpaper has to go. Don't know of anything that will stick to it over the long haul. You will have to peel it off then fix the damage. I've skimmed over walls with even rough tile mastic on them with very good results. Use drywall topping or taping compound (don't use the quick set stuff, it is about impossible to sand!) and a wide drywall knife, or a trowel if you are real handy. Skim it on in thin coats, give it a quick sanding between coats. Sand, prime then decorate. Sometimes there is no good shortcut.