As long as there are no issues with any of the materials used in the mfg of the file cabinet (paint properties, hardware coatings etc...), I'd say rock on!
Had a stripped out old refrigerator that got a lot of hard use. Worked great.
Never thought about a file cabinet smoker though. Seems like an OK idea. Given as someone else mentioned, the materials used. Perhaps a good burn or two before using?
I made an "Amish Oven" out of an old toolbox that has a front cover over the drawers. Pulled all the Drawers out and made a rack that can be set at different levels by using the different Drawer slides as the supports.