Usually filing a motion to dismiss on behalf of a party would be an initial pleading that would constitute an appearance on behalf of the defendants for whom the motion was filed. But it will depend somewhat on the wording in the motion. If the attorney has been retained by all the defendants to represent them, then the answer is no--the lawyer does not need to file a notice of appearance in addition to filing a motion to dismiss.
This answer does not constitute legal advice. I am admitted in the State of Arizona only. This advice is based on general principles of law that may or may not relate to your specific situation. Facts and laws change and these possible changes will affect the advice provided here. You should not rely on this advice alone, and nothing in these communications creates an attorney-client relationship.