From Snow's end, I think that if Yukine knew, it'd be through accident - I don't think it's something she'd advertise, and certainly not to a bb who wants to be a hunter. She'd just try to teach him the best she can and also teach him that morality is grey~~~ not all vampires~~~~ etc. But if he were to know, it'd be because he witnessed something vampire-y happening.
Which I am down for playing out if you wanted to go that way o3ob