Wouldn't do them much good. 5.56 FMJ will go through the Kevlar "Fritz" helmet, as it would the old steel pot. Similarly, unless they are using ceramic insert trama plates, very heavy and uncomfortable, a 55 grain .224" FMJ bullet at 3000 fps will hardly notice the kevlar.
Rule #5 for being a good sniper.
5. For a backup weapon, you should have something light, mobile, and able to get you out of a jam. It should be easily carried on your person, such as a TOP M60 E3 Long.