How can I secure a wall-mount server rack?
You can overkill the job as much as you like, but it's easy enough to use a studfinder or a magnet (looking for screw-heads) to establish the location of the stud non-desctructively, or drill some small holes that will be covered by the rack (and which you can spackle) to destructively identify for certain where the edge of the stud is, and thus infer the center. Given an inch and a half of surface, you don't have to be too precise not to miss the stud.

I've mounted dozens of wall-mount racks and never bothered with more than a studfinder and/or magnet, and not one has fallen off the wall.