There is a whole theory! http://www.dracomalfoyisawerewolf.com
It is never reveiled either way if he is an actual death eater or a werewolf. But some smart folks put this together which explains why he is always sickly and visiting Snape(wolfsbane potion). More sickly than the stress of having to get death eaters into Hogwarts and killing​ Albus Dumbledore before the end of the school year!