In the past, we've asked 1 or 2 campers to "hide" during fire drills. We have told the campers where to go, usually the stall in a bathroom or something. Generally these are places where the counselors "should" look, but sometimes skip.
Typically we'd then send the counselors back out to find the missing camper, if he or she hadn't been spotted before, and the camper would be found quickly thereafter.
Never, once, did a counselor protest this as an unethical practice. If anything, this makes our counselors take their responsibilities more seriously in the event of an emergency drill. So long as you don't put a camper in a place where he or she will never be found, I personally think that this is reasonable.
