I don't think the elm would harm the snake, but make sure you disinfect it before putting it in the enclosure. You can either boil it or bake it in the oven for an hour or so.
I personally don't give my snakes anything to climb on. The hatchlings can climb fairly well, but such a heavy bodied snake is likely to fall. Also, if they ever poop on it...well have fun cleaning!![]()