The salt & sugar are needed to draw moisture out of the meat, make a brine, then soak the flavors back into the meat.
That being said, If you make your own rubs it is easy to reduce the sodium. You buy the individual herbs & spices and mix them up. I have some salt free seasonings that I will add salt to to use as an overnight rub. When grilling, I usually do without the salt.
You used to be able to get Potassium Chloride instead of sodium chloride. The taste was a little different than Salt, but it reduced the sodium. I don't know if the potassium is bad for you too, or not.
Mrs. Dash has several varieties of seasonings now, as mentioned above.
The Spice Hunter has quite a variety of Salt Free Blends. My local Giant Eagle used to carry them. I don't know where to get them not online around my area.
Penzeys Spices also has a bunch of salt free spice blends available.