## Yes, it has to make an attack roll

This is no different from hitting an unconscious or an incapacitated creature, or from hitting an object: in all of these cases, you still have to make an attack roll. You can always miss — you are in a high tension situation in combat. 

The vampire can only bite a victim that is willing, for example because they were charmed by them first, or that is grappled, incapacitated or restrained, as the text says. For grappling, the vampire also has the option to do so with its unarmed strike, instead of dealing damage with it.