1. Yes, Nero is immune to Visions. A side battle card moves a character from the main battle to a side battle, and immune characters cannot be moved from the main battle while they are still immune. So the side battle shouldn't have happened.
2. Grapes only shuffles cards in the current battle (in this case the side battle). So assuming nothing else happens in the main battle (Christian Martyr, Unholy Writ, Gates of Hell adding a new character to battle, etc.) then Micah would win the battle.