The only reason I would doubt it is that Kizaru is a cog in the machine so what makes him a conqueror?
Now, on the other hand, Kizaru is an admiral, so he can have conqueror qualities for being at that position.
You have to be willing to conquer the marine to be an admiral.
I wouldn't be surprised if all admirals use conqueror's haki, even conqueror's coating.
That would make sense and we could even guess that Coby may become an admiral when he gets conqueror's haki/coating.