My son is red-shirting and has practiced and thrown pretty much like any other pitcher, with regular bullpens. He's thrown in inter-squad scrimmages all during the spring, although those scrimmages have decreased greatly as the season progressed. He has travelled to some away contests and dressed in uniform for games. All three red-shirts travelled to, and dressed out for, the Conference tournament, and are travelling with the team for the final few games being played after school ends (today!). The red-shirts seem to do everything but play in the games-team breakfasts, running, pre-game warmups, etc.
The red-shirt has gotten "tight" and he's very anxious to pitch in real games during summer ball. The coach indicated to me when the red-shirt decision was made that he'd pitch plenty in the spring to be ready for summer ball and that seems to be the case, although certainly summer ball "real" games will be different from inter-squad scrimmages.