I've toured a '60s era Cold War diesel-electric sub that's been a museum for ~20 years, and it still absolutely reeked of diesel. Combine that with the smell of a couple dozen dudes that haven't showered properly in weeks, and your answer would be not good.

The long-term health outcomes are probably significantly worse for people that served in diesel subs than nuclear because of the constant exposure to fossil fuel volatiles. Just being in there for a 20 minute tour made me feel like I just smoked 20 cigarettes.