Some really extreme degree of salinity may also inhibit C botulinum spores from sprouting and reproducing, but I’m pretty sure that even the relatively large amounts of salt used to preserve “salt-preserved” foods itself isn’t enough and that it’s the lactic acid from the lacto-fermentation that does the job, not the salt… The spores themselves can survive pretty extreme conditions, but the live bacteria are much less “tough”, even when the “no oxygen” condition is met. It doesn’t take much acid, for example, to inhibit sprouting. Which among other things is why it’s safe to can “high acid” foods only in a boiling water bath, and why non-infant humans and other animals can ingest the spores without danger; our stomach acids inhibit the sprouting long enough for other digestive enzymes and whatnot to break them down completely…
As far as heat is concerned, though, I daresay it’s not something to rely on a regular basis, but fwiw, the toxin the live bacteria produce, which is the actually-harmful thing, itself isn’t very heat stable (unlike some other food-borne bacterial toxins). Boiling temperature in the presence of oxygen for (at least) five minutes is supposed to be enough to neutralize that…
And last but not least, re the actual thread question, outdoor, ground-grown onion/shallot tops are tougher than scallion/green onion greens, or even the sprouts of onions left to sit around too long at indoor room temperature, so I don’t know that they’d work out as well everywhere the the latter do, but I’ve always routinely used at least some of the tops along with the bulbous part of the plant, except in relatively rare circumstances when one or the other is more appropriate - in salads, sauteed/stir-fried, whatever. And fwiw, I first encountered a true scallion pesto (made with the whites as well as greens, but no other herbs) tossed with small shrimp, served cold as an appetizer at Chinese restaurant. (I have no idea if it’s at all a traditional recipe, but the restaurant was fairly authentic Szechuanese at the time.) And it was simple enough that I was able to reproduce it quite well at home, even though I’m not usually great at dissecting and reproducing more involved restaurant dishes I’m unfamiliar with… I might have more detailed notes somewhere, but offhand what I recall was basically just blending whole scallions chopped up with just enough oil to make it “saucy” enough to coat the shrimp evenly, plus a decent pinch of salt.
