This is a question that's bothered me for a while now. According to exrx and a couple books I've read, the serratus is responsible only for protraction of the scapulae, and other similar motions. Therefore, movements of the spine could not be influenced at all by the serratus muscles. And pullovers and chins would only work the serratus in an antagonistic mannor.
Exrx has "incline shoulder raises" listed as the only isolation movement for the serratus muscles. Overhead compound movements such as overhead presses and upright rows, etc (any movement that would retract the shoulder blades), would effecivey hit the serratus muscles. Also, strangely enough, the lower traps are also very misunderstood muscles in the same respect.
Now I'm no kinesiologist, this is just my educated response. If I'm wrong here, someone please chime in here and let me know why.