The concrete can crack during the lifting process, it is not very common however. Generally when a crack occurs in a concrete slab during the lifting process it is because the slab bound up on something as it was lifting, typically an adjacent piece of concrete or a concrete foundation wall. This is another reason why it is important to have an experienced technician lift your concrete. I am very aware of what causes concrete to crack during the lifting process and always do my very best to prevent that from occurring.