You are not suppose to burn poison ivy (or poison oak) because the agent that makes them poison is contained in oil, and fire makes the oil into vapors, which you then breathe, and end up in a world of hurt.
Poison plants like datura and not oil, so the oil thing won't happen....however, I do recall hearing that people try to smoke some plants in that family to get high, and end up killing themselves.
If you only have a small amount in an open space, it should be fine.