If you dont seal the rub strake to the hull, water will accumulate between the two and will eventually permeate through the wood and thus turn it 'dark/black' must faster. Also trapped moisture 'behind' the wood will especially cause the coating to begin to 'lift' at the margin of the wood nearest the hull. Very best is to 'encapsulate' the strake with epoxy on the side that touches the hull, then affix to the hull with 'caulk'.
Simple answer: seal it, standard "Life Cauik" that is 'colored' (teak, mahogany, etc.) will work best and will be the 'least obvious'.