all marshmallows (unless specifically for vegans, like sweet and sara) have gelatin to retain their shape.
BUT if you are vegetarian, and not vegan, marshmallow fluff is vegetarian (but contains egg whites, so not vegan)...and since its already maleable, is actually easier to make krispie treats with.
Smuckers marshmallow sundae topping is actually vegan! tho i sometimes find it hard to find.
and yeah, recipes exist out there that use pb, rice syrup, etc etc. not quite the same, but still yummers.