A Ouija board is just ink on wood (or cardboard-like material). It's a tool like a pendulum, scrying mirror, etc. The tool itself isn't what has the "power" (outside of whatever energies are infused in it from frequent use by the user). The "power" is in the user (you)... the board is just the tool you are using to establish communication. So no, I don't think it's dangerous to bring a Ouija board to an old cemetery.
However, I do think that if you don't know what you're doing, attempting spirit contact CAN be potentially "dangerous" (regardless of where you do it... cemetery, your bedroom, whatever). If you're strongly drawn to this grave, instead of jumping into attempting to contact the spirit, maybe you can try meditation first. Establish a way where you can ensure your safety (a psychic bubble of protection... a safe place your mind can go to during meditation, etc). Once you feel confident that you are prepared and knowledgeable, maybe you can try meditation in the cemetery next to the grave. It might be nice to leave offerings as a sign of well-meaning. Go from there.
Take it slow. When you feel ready and safe in attempting contact, then you can use whatever communication tool appeals to you (Ouija, pendulum, whatever). There's no need to rush it.