Why isn't anyone speculating a fight between a SH member and a CP0 member? Do you think they prefer to kill Who's who more than to kill/capture Robin? If Jinbe is fighting a CP member then why not Brook too, so that every member has fought one.
If that's the case, why Oda hasn't started this yet? Well maybe he needs them for the story for now to count the samurai and the Beast Pirates, but when will they start making their move?
As for haki, i think all of the SH members should have it by now..