Daimoku is Dharma, not Buddha.

Kanjin Honzon Sho: "Entrustment means: It is this Sutra that is only entrusted to the Bodhisattvas Who Sprang Forth From the Earth. . ." (STN, v. 1, 717) 

The meaning is clear. The Daimoku is the Dharma entrusted to the Bodhisattvas Who Sprang from the Earth. Such an interpretation agrees entirely with the Sutra and it is reasonable. The Eternal Buddha, who is ever present but hides His Presence, entrusts His Dharma, "Namu Myoho Renge Kyo" to his disciples from the most distant past. 

On Rebuking Slander and Eradicating Sins (Kashaku hobo metsuzai sho) says, "During this period of twenty-two hundred and more years, worthy rulers and sage rulers have honored painted images of Shakyamuni, the lord of teachings, as their principle object of devotion. But although they have made depictions of the Buddhas of the Hinayana and the Mahayana teachings; of the Flower Garland, Nirvana, and Meditation sutras; of the theoretical teaching of the Lotus Sutra and of the Universal Worthy Sutra; of the Mahavairochana and the other True Word sutras; and of the Buddhas Shakyamuni and Many Treasures of the Treasure Tower chapter, the Shakyamuni Buddha of the Life Span chapter has never been depicted in any mountain temple or monastery anywhere..."

Daimoku is Dharma, not Buddha.