You can't get dutch disease when you have a large underdeveloped sector that can (and will) be modernized with very high reliability. Dutch disease is about an imbalance where domestic production outstrips domestic demand. But the underdeveloped North Korea would be a huge, practically bottomless pit of domestic demand that would last for decades as North Korea was built up to South Korean standards and the North Korean people given basic education and standards of living. You would see Korea run very large trade deficits as a natural product of this development. But such deficits would be completely sustainable because they are matched with increases in the productivity of the undeveloped North. This matches the pre-80s debt development framework where trade flowed from the developed countries to the undeveloped ones, except South Korea doesn't have any of the pitfalls that lead to this framework falling apart. South Korea is capable of protecting Korean economic sovereignty, has v. solid credit and has a political environment that is very adept at promoting development (one could even argue that they are too development oriented right now, but a unification scenario would certainly absorb the excess and then some.)
Whether or not North Korea has natural resources is pretty irrelevant to this. It would be like the natural gas boon in the US state of Pennsylvania. Yes it lead to a boom in 3 rural counties that were lightly populated, but that was irrelevant to a state of Pennsylvania's size. What's much more important is the population and the investments in economy wide capital stocks, real estate, inventories and most importantly of all human capital. Compared to those the heavy machinery needed to mine billions in natural gas is a drop in the bucket.