I have tested this extensively as my game requires FOV 17. (very close to orthographic)
It seems setting low FOV's screws up the engine's depth buffer, there are no ways to set camera clipping masks either.
This means AO and dynamic shadows will be seriously broken the lower FOV you use. (see image below)
As much as I like UDK, this is a pretty big limitation which unfortunately prohibits me from using this engine.
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Did you check out this thread: http://utforums.epicgames.com/showthread.php?t=709682&page=3