If the stump needs sealed, then it shouldn't be used. As for kinds of woods, there are many that have been used, many you can't, and some that I'm sure haven't been tested. I've used many kinds of wood, but the only stuff I could positively identify was osage orange (hedge apple tree).
"This hobby is about 10% what you know, and 90% experimentation." - Lon Heim (DartMan)