In iOOTP warming up a reliever is disabled (they always come ready into the game).
iOOTP (or OOTP for that matter) do not contain any sort of comeback code. People often think that because they get mad at the own players (I know the feeling, I played in Online Leagues for a long time and cursed my players a lot
) and a few bad outings will always stick more in memory. But just look at the 2012 Redsox, they are a pain to watch, no lead is save until the last out is made.
On a related topic (because I see it a lot): the star ratings are based on position, so a 5-star Reliever is much more common then any other 5-star player with a different position).