Can't hurt, but it isn't 100% necessary. I can't say that I know of a single time when my gun gave me away, usually it's any one of ten thousand other blunders that get me busted on stand. I have wraps on a lot of my calling weapons now, but only started doing so a few years ago, can't say my success rate went up much, but I do it.
If you have the wraps, it sure won't hurt, but I wouldn't stay home just because my rifle wasn't camo'd up.