[Don has to ponder this for a while. Training is such a central part of ninjutsu - the only way to learn it - that its acceptability is taken for granted. Bushido certainly states that it's dishonorable to fight dirty in a friendly sparring match, but so far as Don knows the codes nowhere state that katas and sparring, in and of themselves, are ethically permissible activities.]
[Action]
Well... yes. Diligent practice is a virtue.