He is no longer a player or manager. He is John Q Public and betting on baseball is ok for John Q Public.
Now if they want to make that a condition for his getting into the hall of fame, sure. But no one has said that. At least I have never heard about it.
Unless you’re Willie Mays or Mickey Mantle
Barred From Baseball: Rose Is Most Famous, but He Is Far From Alone
http://www.nytimes.com/2015/12/15/sports/baseball/others-banned-by-major-league-baseball.html?_r=0