The type of bead, steel or Kevlar, has no effect on pinch-flat susceptibility of a tire. Pinch flats occur when you hit an obstruction hard enough to collapse the tire far enough so it hits the edge of the rim. The tube, caught between the tire and the rim, gets punctured in two places right across the rim width from each other (the resulting two closely spaced holes are why they are also called snakebite punctures).

The preventative is to run sufficient pressure so you never collapse the tire completely. That required pressure depends on rider weight, speed, what you hit and tire size and pressure. Larger tires and higher pressure both work to prevent them as does a careful riding style.