mixing male and female ferrets

Are they both neutered? If so then being male of female is pretty much irrelevant in how they'll interact. When introducing any ferrets regardless of gender there is always a risk that they wont get along. And there will usually be a level of rough play as they sort out who's dominant, and scruffing and dragging seems to be a big part of that. This is perfectly normal. The general rule of thumb regarding rough play is to leave them too it unless one of them is screaming, pooing or bleeding. If any of these three happen then its usually gone too far (though I have heard of some ferrets who scream automatically when they start to loose during play, without being hurt). Otherwise they are probably ok. How often do the get to interact with each other? Do they have seperate cages at the moment or are they living together? Is the only interactiong they have this rough play? How is she when he lets go of her neck, does she run and hide from him or is she still happy to be around him?

Sorry for all the questions but it makes it easy to figure out what's probably going on if we have more info. Also as a side note, if they aren't neutured then its probably a good idea to sort that out sooner rather than later. Unless you're planning on breeding them, in which case you should really look into everything involved in that before you let them mate, its a big committment.