Short Answer: No
Jacob deGrom has been the best pitcher in the National League this year and finds his name swirling with rumors. He’s also not the only player where this is a possibility as Manny Machado is also in trade talks. While It remains incredibly unlikely that deGrom will be traded, it is very likely that Machado will be traded, possibly before the All-Star Game.
This happened to Jeff Samardzija in 2014 when he was traded from the Cubs to the Athletics. At the game they put him in a National League jersey, gave him a generic hat and named him ineligible to play.
For Major League Baseball, this situation can leave two markets with no representatives in the game. In the rare circumstance where the Mets trade deGrom, a major market team will have no one in the game. In the likely circumstance that Machado is traded, the closest market to the All-Star game, Baltimore, will be without a player.