The researcher that leaves the military takes with them general skills in reverse engineering and exploit development, but they cannot use specific 0days they know about from their military service. The specifics of everything done in the military is classified. People told me they couldn't mention in job interviews some of the skills they have because it's a secret. Like, if someone developed this Turing complete architecture on top of jbig2 decompression while they were in the military, it would be considered a secret that cannot be revealed.
> They cannot use specific 0days they know about from their military service
Of course they can, it is just illegal and might be classed as treason or similar.
Remember we are talking about getting exploits for nation states here rather than just some regular company - hiring spies is part of standard operations for the intelligence community and would be a valid zero-day acquisition strategy (depending on the protection offered for NSO by Israel).
