No, Martin would have been convicted. There were witnesses placing Martin on top during the fight. Martin had no visible marks from being in a fight except for being wet and a single gun shot wound. That is hardly someone who has to defend themselves. Had Martin possessed a gun, and all else being the same, shot and killed Zimmerman, he would have been convicted and it wouldn't have made the news. The jury also would have been told of Martin's background (which wasn't the sweet choir boy people want to pretend he was in the media). He had a history of being in fights, he was under the influence of an illegal substance, and he used a racial slur towards Zimmerman slightly before the altercation took place.
'Under the influence of an illegal substance' is a false description if I understand correctly there were 'trace amounts' of marijuana.
Marijuana does not increase people's tendencies to violence, it does the opposite, and trace amounts do not affect behavior.