We had leather furniture in our last house, and two cats who had back claws. They did not try to sharpen their claws on the leather; however, the problem we found was that the cats would chase each other and "push off" the couch with those back claws. It was especially bad on the top of the sofa, but we also got some of those marks on the cushions.
This is more of a problem when you have more than one cat; however, even one cat can be startled while on the furniture and it is only natural for those back claws to come out when he/she takes a flying leap to safety.
Our vet had assured us that there would be no problem with leather since our cats were missing their front claws; he was wrong.
Oh, and I would also be very cautious about a leather/poly blend. I have heard that they don't hold up well. Even with leather, there are different grades and some of the less expensive grades do not hold up. Our furniture was a high grade, so the cat scratches did not cut all the way through or cause peeling; however, the scratches themselves are deep enough into the colored leather that there is no way to make them invisible.