I wouldn't describe Buddhism as atheistic. It's more pantheistic or even anatheistic. The existence of gods is not disputed by many Buddhists, perhaps even by a plurality of Asian Buddhists. Certainly, very few devout Japanese Buddhists will deny that the Kami of the Shinto faith exist.

Often gods of other religions become incorporated into Buddhism, as Bodhisattvas or avatars thereof. Avalokiteshvara was seen embodied in the goddess Kwan Yin and in the Hindu god Ganesh. And might similarly be invoked as Michael the Archangel as they are a similar principle.