Yes, they do that part ok. And then after they're finished and the military fleet moves away, the AI just rebuilds the same turrets in the same places again. So the perception becomes that clean up drones aren't very useful because they remove debris but... not for long.
If the AI has to use reinforcement points to do this, as Keith said, then it's still worth bringing clean up drones along. But this isn't mentioned anywhere in game so I have no way of knowing the real impact of clean up drones.