Scott - how about soaking it in baking soda and water for a couple of days?
OR
You can make a very good paste using the baking soda and just a touch of water or store bought peroxide - brush it into the fabric and let it set. After a day or two run it through the wash.

If baking soda won't work then nothing will.

I would not soak your vest in scent killer as the peroxide in that stuff could bleach the vest out dramatically.