first of all you only really salt jumps if they are soft because it is too hot. If the snow is too dry, and it is really cold out, use water to harden the jump, not salt.
you can use either kind of salt, but road salts (such as calcium chloride) will work a lot better than table salt. This is because when the calcium chloride dissolves into the snow it releases heat, which melts the snow a little bit, then the rest of the snow essentially "sucks" the heat out and refreezes the snow. It also lowers the freezing point of the snow, which is why table salt will work as well, since table salt lowers the freezing point, it just does not release heat when dissolved.
I remember when we were training in the spring, the coaches all stole the salt shakers from the staff lounge one day, and we used that to salt our mogul jump, it worked well.
