Tangential question: in order to become educated/expert in some field (e.g. IT) one needs the freedom of doing research, free access to information, Internet, thus exposure to "western"/civilized values, human rights, etc... So how NK "produces" such experts behind the iron curtain?
The hackers have a lot more access to information than regular citizens because they need it to do their job, but it would be interesting to know how that affects the defection rate.
Probably higher than your average citizen without access to classified information, but not high enough to make defection a common occurrence that significantly hampers intelligence work. Some hackers may be disillusioned with the system, but most are socially conditioned to accept it as better than the alternative, imposed by external enemies and pressures, or not their problem. Defection is also not unique to authoritarian countries, see Snowden.