Well, it depends the meaning of the word "redshirt". The rules say any counter (a player who has received countable aid, excepting players who withdraw or are dismissed from school in the fall) must be on the 35 man roster, and a player must be on the roster to be part of countable (required) practices.
I suppose that you are thinking of a healthy player who isn't going to compete in games, but who is planning to practice with the team. Then, yes, that player nees to be on the 35 man roster.
On the other hand...
If a skilled player becomes so injured before the championship segment begins that he is unable to play or practice (think Tommy John surgury), and he is not a counter (doesn't have a baseball scholarship), there would be no obvious reason to put him on the 35 man roster. Yet everybody would consider that player to be a redshirt, and wouldn't consider the team to have cut all ties with the player.
I suppose that a strong-armed position player who has decided to become a pitcher might voluntarily redshirt, and workout privately with a pitching coach, rather than taking part in regular practices. That player need not be on the 35 man roster either.
See, TPM understood what you meant, and was able to answer with just one word. By deliberately misunderstanding you, I'm able to take up a bunch of space!
