Here is a video of a yemen battle charge, albeit staged for the camera. The jambiyas are all held in the same fashion as they are in the dances,(further in the video) with the concave edge forward. I never saw a sharp yemeni jambiya though and I would wager most of these warriors' jambiyas had blades made of welded sheet metal. If it really came to using the jambiya, there would most likely be no slicing, only stabbing.
http://www.youtube.com/watch?v=LEzXLpwGPB0
dancing