I think the hygiene aspect is about long-term accumulation of pathogens. You bathe the baby several times a week if not daily. Then you put on a cloth that has been exposed to many pathogens over X time. But I guess boiling shouldn't take a day, since we can pasteurize milk in a very short time.
If you'll be putting them right back on the same kid, then no. Remember, you don't boil the kid's ass to be hygienic. You'll be putting that diaper on an unboiled ass. The diaper doesn't need to be boiled.