Read maybe 10-12 pages of this thread, but I came so far as to someone stating that using the dark side of the force is by definition evil. I don't know very much of the lore, but where does it state that to use the dark side you have to be evil?
An evil person is evil by means of his/her actions. Is a person evil that has a huge passion for power? By definition, no. I say it's possible to draw from the dark side without being evil. To draw power from the dark side you just have to have a certain state of mind, not necessarily an evil state of mind. It might be easier to draw from the dark side of the force by means of evil but imo not the only way.