My wooden peel is untreated.. has a check in it by still works well. I wash it after use, and prop it up so it gets a quick and thorough air dry. I'd also worry that oil would make your peel a little tacky, but in any case you'll need to use cornmeal to get your pies to slide.
Full disclosure, though: I always had trouble getting my pies back *off* the fire, until I got a metal peel (for cheap at a restaurant supply store). It's thinner and works better for getting underneath the edge and sliding them up onto the peel. Now I used my wood peel to build the pizzas and deposit them in the oven/grill, and then remove them with the metal peel. It helps the general work flow as well-- it's a major drag to have a perfect pizza burning while another perfect pizza is sitting on your only peel.