Too much of any good thing can be bad, and unfortunately that does pertain to essential oils. They can coat the scalp and hair if you use too much. But they are healing and I'd have to say a MUST in a dreadies arsenal for healthy hair.
I'd watch how much baking soda you're using. Judge it by how your hair feels when you squeeze it out in the shower. Does it feel slightly tacky or not? Tacky= not enough. Not tacky= perfect. But if you've perfected your BS amount and still have dandruff then yup, EO's can definitely heal in a big way.
Tea tree oil is spectacular but watch how much you use. A little dab will do ya. It is the oilier of all the EO's out there. Don't overdo it. Peppermint is stimulating. Amla is actually a powdered herb which you can make a tea out of and use on your scalp as a treatment. It's a very nice tonic which strengthens the skin on the scalp but it does have a mild softening effect on dreadlocks.