Yes. The ghast would win as the zombie does not have a ranged attack meaning unless the ghast was to float down to the ground the zombie would have no help. It would take an unarmed zombie 8 hits to kill the ghast. The ghast would have to shoot 2 fireballs at the zombie to win. Therefore the zombie has a 93% chance of losing and a 7% chance of winning but the ghast has a 2.69% chance of losing and a 97.41% chance of winning.