I believe the rule states that the pitcher listed on the lineup card must pitch to at least one batter, this is to prevent pinch-hitting for a pitcher before he appears in the game.
I guess at this point all the Nats can do is protest the game if they lose, but I can't imagine the league would uphold the protest since the mistake didn't impact the game.
It hasn't impacted the game yet because it's not over but what if Ricard tosses a no hitter? Rule 3.05 9 (a) states:
"The pitcher named in the batting order handed the umpire-in-chief, as provided in Rules 4.01 (a) and 4.01 (b), shall pitch to the first batter or any substitute batter until such batter is put out or reaches first base, unless the pitcher sustains injury or illness which, in the judgment of the umpire-in-chief, incapacitates him from pitching."