RP who have started games in the real life corresponding season suffer no penalties when you use them as starters in PB. You CAN use a RP who has not started but he will suffer penalties that are outlined in the PB manual.

Because the robot will not start a tired pitcher, there are deceptive advantages if you start a pitcher who you KNOW will be tired at the time of his start in your away game roster (no matter if he's RP or starter). For example: if you can manage to select a tired RHP as your starter when you know the robot will select a fresh LHP in his place... it will be a problem for an opposing manager who didn't bother to look at your roster status page before the game, or doesn't know how the robot will go about selecting a replacement starter. All of the information to counter this strategy is available in the game manual, you just have to be aware of how the robot works.

Cameron.