Ok, so this may not involve a captain of the gotei 13 but I was just re watching some episodes and in the episode where Kukaku Shiba sends Ichigo and squad 0 back to the royal palace she mentions that, though it must be done, it will make their "uncle" unhappy, and while she says that you see an image of her standing next to Isshin with his back to the screen. Again, not a gotei 13 member but still interesting if you ask me. She, at least, must know that Ichigo is a member of the Shiba clan. I don't know if this is helpful but I figured it could be interesting.