[@Juicy] In the sense of one of the species who was bitten by the other? That in itself happening is probably not unheard of, but the two conditions don't really play very nicely with one another due to the serious opposition in their ideal body environment. Vampires have low body temperature, slow pulse, longer digestive tract,  werewolves high body temperature, rapid pulse, short digestive tract. I suspect that a crossover wouldn't live too long, or one 'condition' would overcome the other. Of course if you can come up with a reason a character might've ended up a stable cross, I'd be happy to give it a look. 

[@Spinosaurus] I'm happy to accept different species, so long as they fit the 'could conceivably blend into normal society if they tried' rule. That said, for the sake of this canon's simplicity, 'lycan' and 'werewolf' are just different terms for the same creatures.