I do beleive the potassium in potassium Iodide does contribute to our potassium needs BUT only about 25-30% of the total amount of potassium Iodide is potassium. So if your taking 100mg a day of potassium iodide, than only about 27mg of its potassium.
The RDA for potassium is 4700mg and we all know the RDA for the most part is a joke and usually considerably less than ideal.
Much like iodine, everyone is afraid of potassium but thats not to say you cant OD on potassium because you can so with that in mind you should have some idea of your daily potassium intake is from food before supplementing and for starters shoot for 4700mg a day.