1 - He didn't pass out from Killer's attack. You must have missed all of the threads that proved Zoro fell from a combination of several different factors. Which included poisoning, starving, injury and so on.
2 - Blunt attacks and cutting attacks are not the same.
3 - Killer was only able to hit Zoro because he didn't take the fox a threat at the time and dropped his guard against him. Which caused him to be distracted by the fox, allowing Killer to successfully hit him.