Interesting workaround needed.
Apparently UDK does not have the greatest of doppler effects. In fact, I don't even think this is possible (conventional DSP manner) in the UDK engine.
HOWEVER, I did find a post from a sound designer named Graham Gatheral based in the UK.
Top right, there is a clickable video on how he linked a doppler shift equation in Kismet to the sound needing the effect. It calculated the players position/direction and movement of the sound emitter requiring doppler, to pitch shift the emitter's audio as it flew past.
As far as I know, thats the only way to do this.
My question is...
If you were going to do a bullet whiz-by: Would you create a compressed, dynamically constant whiz by with a pitch shift built in; shifting in pitch from high to low at the same rate that it would take for the bullet's audio radius to pass by the opposing player? Whats the best way to implement bullet whiz-by and/or ricochets off of surfaces?