I'm using the unreal engine and have so far been unable to find the specs required for the sound. E.g bitrate, size, length; and stuff like that.

If you are using the Unreal Engine 2, then the limitations are the same as OpenAL as it uses OpenAL for it's sound core.

The original Unreal Engine uses the Galaxy audio system and shouldn't have any limitations other than the ones provided by your hardware.

Does Unreal Tournament 2004 engine use OpenAL?

AFAIK, yes. Unreal 2004 uses build 2225 of the Unreal Engine, which has OpenAL as its core.