The acid etch would really not accomplish much unless you think there might be external pollutants on the rock, such as oil, tar or something. However it will easily remove organics from the surface as it will actually remove the surface it self.
It is generally used more often to remove a layer of the rock when someone has used copper in a tank containing carbonate based rock. With out some pretty extensive testing though it would be hard to tell just how effective it would be even for that use. I have never been able to read how deeply copper will penetrate into live rocks.
Yes with cooking bacteria does the work, however you still need to periodically remove the stuff pumped out of the rock by the bacteria. Some use active skimming, some use just heavy circulation, siphoning of crud and water changes. I assume once active bacteria has colonized all rock, one would want to keep the nutrient level in the water low, so that the bacteria will only use the nutrients in the rocks as food.
