pretty much. you dont even have to blow anything up with a nuke to be successful.
if nk leadership is insane enough, and knows they have lost the war, all they have to do it blow up a dozen warheads that are just sitting in their storage.
if done right, the entire upper hemisphere would be uninhabitable for a good 80 years.
or NK could just volly off a million rounds of artillary at fukashima. no missile/shell shield could stop that kind of disaster. and it would forget us all.
just by having a nuke, a nation is threatening the world with "if anyone or any alliance invades us, the whole world dies"
you dont need functional ICBMs to do so.