KH helps to control pH... the higher the KH, the more stable, and potentially higher, the pH will be.
Of course, pH is controlled by more than just KH.... CO2, tannins, humic acids, oxygen, fulvic acids, etc can all play a role in pH.
I would hazard to guess that if all other parameters are fine, the snail is likely to do okay in lower KH water. Take my word with a grain of salt though! I don't have any fancy snails! Just your average pest snails.