Can we use .raw image format directly in CV functions?

edit

unfortunately, there is no such thing as a "raw" format, it is, whatever your camera manufacturer is using internally (there is no "standard" for this)

opencv does not have any functions to read or convert that (though it may involve de-bayering), you're quite on your own here.

Will it give a better result?

if the alternative is jpg encoding, -- probably (you'll get rid of the lossy compression and the block artefacts)