The United States defenses are the best in the world. That is a safe place to keep the nukes because the only country near Seattle is Canada, and Canada isn't big on starting wars. The United States has the benefit of geographic isolation from much of the rest of the world. This means that the nukes are safe in Seattle.
I don't know about you, but I'm not comfortable being guarded by a creature that considers a herring to be a bribe. How do we know that there are no rogue dolphins ? You can't do a background check on a bottle nosed dolphin. Between the nuclear stockpile and Microsoft, Seattle could be is serious danger.
Much of the world's nuclear weapons are not be adequately protected. Unfortunately, this is true for the United States' nuclear arsenal too. Nuclear nations must do more to ensure that these dangerous weapons are secure, and can be defended against potential theft or sabotage. Nuclear proliferation is still a major threat in the world today.
No, the biggest concentration of nukes is not being protected adequately by trained dolphins. A huge stockpile nukes being protected by dolphins, trained or not, seems to be dangerous. I would think that the world's largest concentration of nukes would be protected by trained military officers or security guards with guns.