I've had this discussion with two umpire colleagues in the last month regarding players not listed on the lineup card. Both argue that they are illegal substitutes and I argue that it is legal. FED is clear:

Rule 1-1-2: The captain and the coach represent the team in communications with umpires. The captain’s duties can include: 1) providing the umpire-in-chief with his team’s lineup card which shall include the name, shirt number, position and batting order of each starting player, the name and shirt number of each eligible substitute; and 2) informing all players as to special ground rules as announced by the umpire-in-chief. Lineups become official after they have been exchanged, verified and then accepted by the umpire during the pregame conference.

Casebook Rule 1-1-2 SITUATION A: During the pre-game conference, coaches of Team A and Team B hand in their lineup cards to the umpire-in-chief. Team A’s starting players as well as all eligible substitutes are listed on the lineup card properly, but Team B’s lineup card lists only starting players. During the first inning, Team B wishes to pinch hit with a substitute player who is not listed on the lineup card. RULING: Legal. There is no violation or penalty if the substitutes’ names are not listed on the lineup card.

I can't find anything in my OBR references. Can someone help me locate a reference (professional interpretation or rule reference) that indicates that this is legal?

MLB Umpire Manual:

3.1 LINEUP CARDS
Each manager should write the name of each eligible player on the face of his club's batting order card in addition to furnishing the starting lineup. However, a manager's failure to list an eligible player does not prevent that player from entering the game, nor is such failure grounds
for protest, as the listing of eligible players is simply a courtesy.