^^^ I agree with Ole Man Dan - if the wood has been well dried and seasoned, and there's no obvious mold or discoloration on the bark itself, it's fine to leave it on. Along with Boshizzle's example above, I can tell you that the legendary Skylight Inn here in NC uses split oak with the bark on. Most of the restaurants I grew up eating in back in GA also used Oak and/or Hickory with the bark left on.
Of course, no one's gonna fault you for taking it off, especially if you're concerned...but definitely relegate any wood with discolored/moldy/spotty bark to the woodpile for your living room fireplace or outdoor fire pit.
If you've got a good sized load of wood, why not do one cook "bark on" and one cook "bark off" and let us know your experience?