Reply to dragartist
Backend crew on the RJs need to be military. Various international laws and military regs make it difficult to fly "other-than-military" on a military mission. If you have 'civilians' on a reconnaissance flight then you could be considered a "spy" vs. "reconnaissance" mission. Very BIG differences on how that is treated under international law. (One reason you never see "spy" used to officially describe any reconnaissance platform-U-2, SR-71, RC-135s, etc. Only the sensationalist press uses "spy plane" in this context). You can fly members of other services to fill the backend seats if you need the experience, but they need training on the system and equipment. I don't see how that ameliorates the training problem.
RJ crewmembers also undergo all the usual aircrew training: altitude chamber, egress training, etc.
Bottom line: Plan to train the crewmembers you need to accomplish the mission. Having enough linguists in the more esoteric languages, who can be aircrew, is always a problem. In that case you fly with a less than full-up crew.