The Crab Samurai i have mentioned does use the tetsubo, but our DM says Iaijutso duels are only for Katana's, no other weapon allowed. Personally, I agree, Iaijutsu is all about honor, and your Katana, even for a Crab, IS your honor. To use anything else would be dishonorable.
As for Scorpion Samurai being honorable. They are, but even they will throw it away on a moments notice if the dishonorable actions are deemed necessary for the good of the Empire or Clan. Look at the founding histories of the Scorpion, and why the Emperor said that the Scorpion Clan is so necessary for the survival of the Empire.
And Ronin can definitely be a Samurai, just without a master. Usually honor demands they stay alive to fulfill the dictates of honor. Once honor has been fulfilled, and fulfilling it did not kill them, then they can commit Seppuku and die with the honor they deserve.
However Ronin can also be Samurai who have forfeited honor in order to live their now meaningless life. They are to be killed like the scum most Ronin are.
In Rokugan, Ronin can find a life on the wall with the Crab, or can be used as tools by the Scorpion Clan. Or they can become Monks.