Can Buddhists go ... to worship the earth god?

Of course. The land Lord is also a good knowledge. The Huayan Sutra tells that wealthy teenagers visited 53 kinds of good knowledge such as Bodhisattva, Bhikkhu, Bhikuni, Youposai, Youpoyi, Boy, Virgin, Night Sky, Goddess, Brahman, Elder, Doctor, Captain, King, Immortal, Buddha Mother, Princess, Land God and Tree God, and finally got various teachings.