Yes, pomacea bridgesii ususally won't eat any vegetables until they've been in the tank for a couple days and have softened a bit.
It's not that they're stupid, their radula (rasping tongue) isn't as tough as that of other snail species, so they have to have either blanched or cooked vegetables. Or you can just leave them in the tank for a couple days. That's why these snails are safe in a planted tank - they will only eat dead plants.
Most people just throw the vegetable in the microwave in a wet paper towel for 10 seconds or so. Works like a charm.