Adding salt to the oil making potato chips
Potato chips have to be fried in lots of oil. If you are using little, you are doing it wrong and your chips are less tasty than they could be. 

As Preston Fitzgerald mentioned in a comment, salt doesn't dissolve in oil. It could be that it will fall to the bottom. Alternatively, the convection in the hot oil could move it around. But still, the salt will tend to stay in the oil and not cling to the potatoes. Even if an oiled flake meets the potato, it will not stick, the oil will lubricate it enough to prevent sticking. If you salt the raw potatoes instead, the salt will dissolve in their wetness and coat them evenly. 

Your popcorn is entirely different. There, your small amounts of oil, including any salt floating in them, will cling to the popcorn. This is different from frying, where only a tiny fraction of the oil will stay on the potato. Besides, you can't salt corn kernels before popping - the salt will just fall off the hard dry surface. The potato is perfectly salted before.