I am very strongly feminist and I am also a member of the BDSM community. Do I think there is a contradiction? The answer is a resounding "No!"
The way that I see it, as long as the activity is consensual - as long as the parties are adults and mature enough to decide for themselves what makes them orgasm and what makes them feel whole, that the choices a woman makes in pursuit of her sexual satisfaction is her right as a human. Whether a particular woman is Dominant, submissive or switches between the roles, she is simply acting upon what makes her feel like a complete woman and is, therefore, exercising her feminism in the highest regard.