Killer is only there because he follows his captain. Duh.
Same thing with Zoro, he will help his captain Luffy.
Why does it matter if Killer is there or not, or Sanji is there, or Zoro is there or not? They are all underling pirates of captain Kidd and captain Luffy. The captains determines everything, Killer doesn't decide anything, nor Zoro, nor Sanji.
Kidd, Law and Luffy are the only important pirates there, the rest is almost irrelevant.