If I am posting wallpaper, is it still necessary to apply joint compound? I though that corner could be cut because the surface won't be exposed especially if i cut all the beveled edges off and achieve a uniformly thick surface. i thought that wallpaper adhesive would fill the little holes.
Yes you should still mud, tape and sand all of the drywall joints especially if your drywall has beveled edges. Ideally you would also apply a coat of primer before you apply the wall paper as this makes removing it easier down the road, and if you do ever decide to paint it, at least all you'll need to do is remove the wall paper and paint and not have to deal with mudding the joints.
If you don't mud it, the wallpaper is gonna highlight every screw, seam and flaw. It will have air bubbles over every screw and gap. Would look like a real hack job. Anything worth doing is worth doing well.