Well, maybe our "stuff" doesn't stink or our noses don't work that well, but I have never used any additives, or ice cubes, in either black or gray holding tank without any particular problems. I have been in other folks rigs that smell (stink, depending on your sensitivities) of the chemical "fragrances" that have been added. Sort of like the "deodorant" blocks used in urinals in men's rooms. I have, rarely, noticed a slight (emphasis on "slight") septic tank odor outside the rig in certain climatic conditions. Warm days with temperature inversions, for instance. Methinks the "stinky tank" problem may be a bit overblown. Maybe more psychological than real. Who likes to think about living with a tank of raw poo attached right under their living space?
Also, we do not dump as the last thing before heading home from the last campground, or between campgrounds. Leave it in there to slosh around and liquefy. And let the microbes do their thing. A septic tank is called septic (vs antiseptic) because it's loaded with bacteria that eat and beak down the solids. We have a state park with dump station a few miles from home which we visit as the last stop before home, or dump upon arrival at our next camp. It works for us. YMMV.
If you dump too often, or leave the black tank dump valve open when camped, you may develop the dreaded "brown mound." The liquid drains off and the solids get left behind to dry out. If you don't dump often enough your tank gets overfull and you may end up with a clogged drop pipe between toilet and tank. I have experienced both. Neither is happy. You will eventually learn the happy medium.
Bottom line is, if the contents of your tank is sufficiently liquefied when you dump you shouldn't have any sludge build-up problems.