Yeah salt reduces stress and helps enhance the disease treatment. I would suggest 1tbs for every 5gal. You may need to do several treatments to get rid of the flukes. The treatment will stay in the water for about 48hrs, usually less. Do a 50% water change, drop in 7. I would then wait another 48hrs and repeat. A total of 3 treatments over a week should kill em off. Salt will certain help the general health of the fish though, it helps alot with gill function, and disease recovery.
Salt also adds essential electrolytes, whatever they are.