Is killing random people with a lightning bolt used as a handy training mission for recruits into the Secret Space Program (Mercenary Army Program)?

This is very much the case. With having a current membership of over 1 million recruits and given that each one must be put to the test to determine their willingness to kill fellow human beings, and often times more than once, there is a need to spread the targets among the widest possible number of mechanisms, to not create suspicion there is something hidden and sinister working against humanity inexplicably. So they must maintain the cover of things like natural weather, or human conflict, where they can come in and carry out a random killing surreptitiously that will be ascribed to bad luck, prosaic forces, and coincidental timing to be in the wrong place at the wrong time, and so on. So this is done quite frequently, because it is simple and does not require close proximity of the recruit to the victim, as the instigator will be hovering in a cloaked spacecraft and undetectable to bystanders.