The Dark Arts are set apart from other forms of magic by the intent of the wizard using it.
Most magic is neutral and can be used for bad or good. But, some magic is evil in its intention through and through. These spells are often called curses. Curses are spells that are intended to cause harm to another person.
The intent to do harm places that spell in the realm of the Dark Arts. Simply casting a Curse spell doesn’t mean that a person is using the Dark Arts.
The deep, true intention of the caster is what makes the difference.
This can be a difficult distinction to make in many cases. However, understanding the difference between acceptable and Dark magic is of key importance for witches and wizards in training.
Since the Wiccans are not to harm others, they should not participate in the Dark Arts.
Is there a specific name that Wiccans use for those that practice the “Dark Arts”?
While we do not have a particular name for the Dark Arts we acknowledge that there are times when they need to used. As stated above its not what you do that counts its what your intentions are when you do the working. But remember all actions have a reaction which is the price we pay the workings we do. I say this from a none fluffy none Wiccan, Traditional Witch point of view.