You can play as a graduate student as long as you have eligibilty remaining.
Roundingoutthird,
I am in agreement with you regarding 5th year. Very few schools carry 5th year seniors in any sport. The coach is not giving all those redhsirts out because he is going to keep those students around for 5 years. Chances are he is way off his 11.7. and doing the right thing of keeping the player there instead of letting him go. There is just not enough money to go around or scholarships. One of the pitfalls of college baseball. I don't mean to be negative, but one should not think that redshirting is being used to keep a player at school for a full 5 years. Not in any sport. If you are given a redshirt year, chances are you still will be expected to graduate in 4 years, same as anyone else, or be drafted.
Football is a whole different animal. Can't even compare football eligibility to baseball eligibility. The player is kept because he will make a significant impact to the program and that translates into big big dollars.
Montanadad,
Stanford is not the only school that does that. If a coach only expects a player to be there for 3 years, they load up on credits, and sometimes you have no choice but to take them. Bottom line is they want to move you out and not have you hang around forever.