No info on rabbits, but this is for dogs and cats if that helps.
From the Pet Poison Helpline:
Tea Tree Oil
Poisonous to: cats, dogs
Level of toxicity: Generally moderate to severe, life-threatening
Common signs to watch for:
Low body temperature
Weakness
Walking drunk
Inability to walk,
Tremors
Coma
Increased liver enzymes
Death
Tea tree oil, also known as melaleuca oil, is an essential oil produced from the Australian tea tree (Melaleuca alternifolia) plant. Tea tree oil is known for its antifungal and antibacterial properties, and possibly for its antipruritic, anti-inflammatory, and antiparasitic effects. Tea tree oil is often found in varying concentrations and should never be used on pets. As little as 7 drops of 100% oil has resulted in severe poisoning, and applications of 10-20 mls of 100% oil have resulted in poisoning and death in both dogs and cats. Clinical signs include a low body temperature, weakness, walking drunk, inability to walk, tremors, coma, increased liver enzymes, and even death.