My MIL or mother never have smacked my children. Ive never really been around MIL long enough for the girls to misbehave, thus seeing her reaction. But my gut says no, she wouldnt smack.
My mum has looked after the girls on the odd occasion, maybe raised a stern voice now and then, but no, hasnt smacked my girls either.

TBH....i would be horrified if they did.