Trapper,
I beg to disagree i'm afraid, that if someone is iodine-sufficient, then they would still need to supplement with the hormone precursor of Vitamin D.
Food sources of Vitamin D are woefully inadequate, and where the sunshine-vitamin can be definitely in short supply in the Winter months, and/or if adequate sun-exposure is not possible in the summer months.
However vital Iodine is to good health (and it most assuredly is) this cannot compensate for receiving adequate Vitamin D via supplementation.