Rescue Rabbit cannot activate its effect when Rivalry of Warlords is active, unless the controlling player has two Level 4 or lower Beast-type Normal Monsters of the same name in their Deck.
If they do, however, then since Rabbit is no longer on the field when its effect resolves, they may Summon monsters of any Type (assuming Rabbit was the only monster they controlled).
If they do, however, then since Rabbit is no longer on the field when its effect resolves, they may Summon monsters of any Type (assuming Rabbit was the only monster they controlled).