You have never watched "The Prisoner" have you? Patrick McGoohan played a character who was also had the "name" of "Number Six" in that show too...
No, I wasn't aware of it. But it seems that the creators of BSG were. According to “Battlestar Galactica: The Official Companion”, written by David Bassom, the character was named "Number Six" after his character, as an indirect honor.
