As has been pointed out, the "Koufax card" is a "holiday" card, not a Christmas card. Even if it were a Christmas card and Koufax did not celebrate Christmas, there is no reason why he could not send a Christmas greeting to someone who did.
“My grandmother was a huge Tiger fan who was always glued to the radio listening to Ty Tyson’s play by play. Sometimes Hank (Greenberg) would drop me off at the house in his Silver Hudson Terraplane and talk with her. Believe me, it was her moment in the sun,” Collins says. “For years he would send us a Christmas card.”
http://blog.detroitathletic.com/2010...rip-collins-2/