I wonder whether the Salem hypothesis -- more precisely, the fact that the Salem hypothesis is interesting -- is largely a base rate fallacy. If there are a lot more engineers than, e.g., physicists (which I think there are), and if creationists will claim "scientific expertise" for anyone doing anything even vaguely sciencey, then even if there's no interaction at all between domain of expertise and susceptibility to creationism most "scientific experts" who are creationists will be engineers, just because most "scientific experts" will be engineers. (My impression is that a better version of the Salem hypothesis would say "If a creationist touts scientific expertise in a supporter, said supporter is likely an engineer, computer person, or medic" -- and now take a look at the graph at http://www.intuitor.com/physics/ScienceCareers.php .)

Is there more going on than this? Maybe. It's possible, e.g., that the cleverest scientific-ish people gravitate to fields other than those and are less likely to be creationists. Or that something about the kind of problem-solving engineers have to do fits somehow with creationism. (I've heard a similar explanation proposed for an alleged prevalence of engineers among terrorists.) Or something. But I'm not at all sure that it's not just a matter of base rates.