That's a disingenuous argument. If you're building nuclear weapons for a hostile government, you're as much a target as anyone else. It doesn't matter if you're a scientist or a solider.
Like I said below I don't think it's ever justifiable, and it goes both ways. There are thousands of good scientists working with the DoD. The US is technically at war. However I do not believe their scientists should be considered legitimate targets.
It's also debatable as to whether they're developing a nuclear weapon.
