Ok, so the real life M14 was rated #2 for best "battle" rifle. It also just so happens that for the longest time, this rifle was used for spotters, where available. Why would I suggest this gun for an airsoft spotter. My brother has a TSD M14 (which I have used in my fanatical obsession of guns (Plus I paid for half)), very accurate, nice range and good rate of fire without having to upgrade any parts on it. The so-com versions are smaller, which might be better for a spotter, and most local surplus stores will sell gun wraps for you and your sniper.
But an important rule to remember is, "Even a spotter is still a sniper first."
Carlos Hathcock himself spent time as a spotter, even after he was considered a good sniper. Always remember that even as a spotter you should be just as good a shot, if not better than your main sniper. One shot, one kill.