An NBA owner can also be the GM but they cannot coach or be a player. This is prohibited by NBA rules and is the reason Magic Johnson had to sell his small percentage of the Lakers when he coached them a few seasons ago.
Only in the NHL can an owner be a player. Mario Lemieux did it with the Pittsburgh Penguins a few years ago.
I don't know the last time an NBA owner was also GM, but in the NFL, Jerry Jones holds both titles for the Dallas Cowboys.