Yes, nuclearized countries are right to complain about a nuclear armed North Korea. North Korea is led by a mad man who positions himself as a literal god to his people. Any person that does such is not fit to lead a nation that has nuclear capability and must be stopped.
I do not think it is acceptable for countries who have nuclear weapons to complain about North Korea having them. Nuclear weapons are scary in the hands of anyone. Who is to say that they could not be misused or given to the wrong person by any country? A small nuclear weapon can ruin a whole city. Think of Hiroshima and Nagasaki. Should any country have access to weapons that cause such devastation? I don't think they should, and if they do, they shouldn't complain about North Korea having them.