Yeah, and for what? It's not like South Korea has some supreme leader that has grip on everything going on within the country and is the centre of power who wants to hide inside a deep bunker in case there's a hot war. It'll be useless.
South Korea also happens to have power/control nodes, that out of necessity hide in bunkers to allow access to command and communication facilities.
In case of war South Korean military is of course subordinate to US command, but that command is military, not everyone, and it is also a target.
Implication that ROK politicians are proud Spartans and want to live less than Kim is questionable, since literally all of them end up in prison for corruption after their terms. They are people, and most people in power enjoy their lives.
Not so long ago North Korea tested 2.5 ton heavy warhead and recently couple times of 4.5 ton.
On ballistic missiles much smaller than Hyunmoo-5 and North Korean's have Topol-esque ICBM.
If they wanted in response they could just use 1st stage of it and mount 20 ton heavy warhead.
The point of hm-5 is not just to lift warhead over the border, it's to slam it downwards, vertically from a lofted trajectory, piercing some very high level fortifications w/o need for nukes.
I frankly doubt it's enough, but South Koreans will know better than me.
In any case, no one wants to end up as Russia, which simply can't penetrate Soviet deep facilities because it simply didn't prepare for that.