Pagan is such a broad term that its difficult to answer that question. If you believe in some of the things that most pagans believe in, such as reincarnation, karma etc., then dealing in dark magic (or white magic for that matter) will have reprocussions. Anything you do comes back to you 10 fold, or at least that is one of the basic tenents of Neo-paganism. But the faith itself is kind of a mish mash of different beliefs and so no one pagan holds the same exact ideas.
But I have to ask...what exactly are you considering dark magic? From what I understand, the only thing that is considered 'black' magic is using magic for selfish personal gain or to harm others.
I'm curious to hear other opinions on this one. :)