Indeed, they're a very interesting exception to the general rule about healthy people not getting significant irradiation. Pilots in particular could be a useful group to study given that they have mandatory medical checks; however, I'm not sure that the sample would be large enough to yield any statistically significant results, even if the privacy issues could be circumvented.

(Also, you run into socioeconomic confounders: Can you find another population which has both the same irregular schedules and the wage scales of pilots?)