Steroids have never really been an issue in Cuba, I would expect them to be extremely difficult to acquire even if there is someone that can supply the players. You don't need to use PED's to hit well in the Cuban National League, however whether they got some under-the-table substance once they defected is entirely possible. Players like Abreu, Cespedes and Chapman were already beasts in Cuba (and international play as well), so it's not like for them to succeed in the MLB was completely out of the blue, good baseball players will be good anywhere they play.