You should ask the question, what safeguards would be different than for a private company. Vastly different and more secure. Many things make some people different than others.
People in the government that are in positions to have access to sensitive areas like nuclear weapons and technology are vetted, monitored and routinely moved around. Genetics and mental disposition are another two obvious answers to what makes someone different than another, but I assume you know that.
I'm not asking how people are different, I'm asking how two people, who might otherwise be the same with the same interests, are different from the fact that one works for the government, and one works for a private sector?
(while not defending what they do, private military companies have quite a lot of training, vetting, and security as well, as do nuclear power stations).
What I am trying to get at is that you seem to be perfectly ok with allowing some people to own nukes, while not allowing others, and since I'm sure "because they work for a government" is not your ONLY reason for that claim, I'm wondering what the other reason, besides under what system of bureaucracy they work, that is. And if the entire reason some people whould have nukes and some shouldn't IS only because some people get their paychecks from government and some down, I want to know what makes the people working for a government different from those who do not? (besides being underpaid and likely undesrkilled I mean)