one note, many rocks should not be used in sawlt water for reasons which you seem to know about.
Now, of the safe few, I would cure it and cycle it before adding it to the tank. Because dead or unlive rock, has a bad habit of creating instability until it does become saturated with life(bacteria), and this will often last well past the initial cycle. And after that, it can be a problem for algae too. So just use caution and make sure it is WELL cured before adding it.
tufa is a good substitute,and can be bought at a landscaping business for about a dollar pound in most areas.