Someone told my dad their doctor said you can "have as much sea salt as you want." now he eats it all the time. is this true?

Normal kidneys: Yes. If his renal function is normal. And his blood pressure is controlled or normal.

Too much salt: Too much of any salt(sodium chloride) may lead to high blood pressure and/or fluid retention. There is plenty of sodium chloride in much of our foods and i don't recommend adding extra salt on most foods. There is nothing magical about sea salt although some people feel it tastes better than mined salt.