b) it would fall squarely into the category of "really not recommended by food safety types", for the same reason that the safety of home-canned pumpkin puree or pumpkin butter cannot be guaranteed. It's an extremely thick puree and it takes industrial type processing to guarantee that sufficient heat has penetrated all the way through all of the jars.
A further problem wiht hummus is that it is normally eaten cold, so will not recieve further cooking the way even pumpkin puree probably would. (Boiling food hard for 10-20 minutes after opening the jar is good, although not necessarily 100% infallible, insurance against any botulism toxins that may've gotten going in there)
So, I sure wouldn't do it, and it would probalby be a real good idea not to give any cans o' hummus to anyone else, but it's a free country, more or less
(e.t.a if you are dead set on doing it, it would probably help to minimize the tahini or just wait and add it later when you're ready to eat, and to add as much lemon juice as your tastebuds can stand. I still wouldn't DO it, but, those things would at least be steps in the right direction)
Or could you can the chickpeas whole, maybe with the garlic in bigger chunks, and then when you want hummus, drain it and mash it with the rest of the ingredients?
Even a storebought brownie mix requires adding three ingredients, so it would be reasonable.....maybe. Not what you are hoping for, but a compromise.
What about freezing it? I'd do that in glass, or the garlic might flavor everything else in your freezer.