Yes it can and wood is the best material for diffusers. This will mostly diffuse upper and high frequencies - since it has a shallow depth, bandwidth will be narrow, but better than nothing...and cheap.
diffuser
can this be used as a diffuser on the wall behind the speakers?
https://www.worldmarket.com/product/mosaic-wood-panel-with-shelves.do?sortby=ourPicks
https://www.worldmarket.com/product/mosaic-wood-panel-with-shelves.do?sortby=ourPicks