As shown in Punk Hazard, they have a chance of reincarnating in fruits that are nearby them. I'm assuming that some characters just get incredibly lucky and manage to have a fruit spawn near them after either killing said fruit's user or being the user that died.
Also, the fact that Moria suspiciously had both Gil Bastar's corpse, and also had a hench(wo)man with his fruit under his command, seems to be grounds for him killing Gil and keeping the corpse.
Crocodile killing Ganzui has a little less going for it, but given that he clashed with a different Rocks Pirate (Primebeard) before, it's not unlikely he had went after other members of the group beforehand and maybe got a little cocky because of it.
These would serve as solid hypetools for these characters, and wouldn't feel weird since they are Warlords and people like Ganzui are far less important and powerful than people like Big Mom or Shiki, so them losing to Warlords isn't that surprising.