They certainly are. Unlike Iran they actually have nuclear weapons, are politically unstable and have a brutal Stalinist regime willing to use them. They also have a very large and strong military force where as Iran's is so weak they can't even handle a military pip squeek like Israel.
Which is completely irrelevent as no one in their right mind wants either regime to have muclear arms. So enforceable and verifiable agreements that reduce or eliminate their nuclear arsenals are good ideas and diplomatic engagement to accomplish that are very, very good things. To say one agreement is good and the other lousy where one (Iran) has lived up to their agreements and the other (NK) has proven untrustworthy in the past. So to make the distinction that Iran is bad and NK good when there isn't even an actual agreement in place is simply partisan political hackery.