* Green olives can also be fermented (i.e. w/ yeast and bacteria, instead of using a lye- or pure-water 'cure'), to remove the bitter compound, and would thus be "pickled" in the traditional sense. These olives are not as green or firm as lye-cured olives.
* Why not pasteurize green olives, if you can do it with black olives? You can, but the heat would cause the green olives to become mushier, people expect green olives to be firm, and ripe (black olives) to be a bit soft. Soft green olives often are less desirable, outside of some specific preparations. (I.e. 'Greek-style' "crushed" olives.)
* Can you ferment, and thus pickle, black olives? Sure, why the heck not? Many Greek styles of black olives are done this way.
* Yes, you can pack cured green olives in oil too, like black olives. Anything to reduce the bacterial and oxygen activity in the olives will help to preserve them.