They do take in iodine, errr iodide. Either way, unless your tank is completely chalk full of xenia/other soft corals, I would not recommended dosing iodine/ide. It's pretty easy to get the iodine levels off whack, which is toxic if overdosed. After all, that's why "iodine dips" are effective.
For a normal amount of corals, the usual water change amounts will supply all the iodine they will ever need.