I tried making the dressing with only hemp seeds, and it turned out a bit bitter. I didn't mind, and enjoyed the dressing anyway. Adding cashews makes it a bit creamier and the sweetness counteracts the bitterness of hemp seeds.
*I've used different combinations of herbs. The classic Green Goddess is made with tarragon, chevril, and dill, which is a great combo. I also used basil, parsley, and dill. The parsley is a great fresh flavor. I love to use tarragon, chevril, dill and parsley, if I have all the herbs on hand.