I tried using an L9 in Cabin Fever, and it doesn't work unless its headshots, but thats for any sniper in Cabin Fever. Also, don't use the FAMAS, its one gun I know fails for the new fireteam.
Otherwise its fun and gets more gp/exp if you kill lots of zombies. I've gotten up to like 118 kills on it before, and highest streak is 7 killstreak!