Are there other groups or persons besides the ADL who actively oppose Armenian genocide resolutions?

Certainly.

First and foremost, the Turkish government has spent millions of dollars on public relations firms to fight U.S. recognition of the Armenian Genocide, hiring high-priced lobbyists, including former congressmen, to advance their denialist agenda.

Also, various Turkish organizations, the U.S. State Department, some corporate lobbies, and other organizations have long worked against acknowledgement of the Armenian Genocide. Armenian-Americans and others have criticized those groups and persons for some time.