Just about any piece of wood that isn't treated or processed (like plywood or wood you buy in the hardware store) can be driftwood. It won't "nasty" your water. It might release tannins into your water if you don't boil it or bake it or soak it (or all three, if possible) first, but tannins are found in fishes' natural habitats and they LOVE them. A lot of people buy stuff called "blackwater extract" to add to their water to do the same thing that natural tannins do. However, activated carbon in your filter (or filter media) can help keep the amount of tannins in your water down, as well as routine water changes.
I'm curious about your "it doesn't look like it" comment. How does it not look like driftwood? *scratches head*