In case a NK missile is launched towards Guam, the trajectory goes all the way through SK and then through the southern island of Japan. Geographically speaking, SM-3 and Aegis cruisers could be lined up along the trajectory and shoot it down. Not sure THAAD can make it during the missile ascent phase even if it is located near the NK-SK border.
Much harder situation would take place in case that mad hamster would try to shoot at the US continental territory (when/if his stuff is ready for such a trick). The trajectory would go through the Chinese and Russian territories - no business for SM-3, rely on GBI at Alaska only.