I almost never encounter hackers. Sometimes i see hackers "pre-firing" around corners but that may be lag-compensation. There are a lot of hack that i haven't even seen in-game. The magnet or spawn trap hack, account hopping and aimbot are some hacks that i've never seen someone use in-game. So lucky or awesome Wii?
Sometimes I prefire if I know people are over there. Mostly high traffic areas, or if I know there is a camper there, or small corridors. Especially, if you see them on radar first.