I have a load bearing cmu block wall (roof ties into it) that a plumber had to access inside to get to a water line to abandon. To do this he knocked out approximately a 12" tall by 8" wide hole in the wall near the bottom with a hammer (wall is a 10' tall and 8x4x16 open cell block not filled or rebar). See image.
Should I be concerned about the structural integrity of the wall being compromised from a hole this size, or should I add any kind of support to it?
If the loading is just that of a normal roof you should not have any concerns about the integrity of the wall. The rest of the structure of the wall is interlocked sufficiently to overcome this matter hole. How you cover up the hole depends on the use of the area. You could just simply attach a sheet of plywood with anchors to cover it if appearance doesn't matter. If you want to look like the rest of the wall you could buy a couple of blocks, remove the faces and mortar them into place.