In short, yes. The people of Umuofia believe in many spirits. Each person is believed to have their own "chi" or personal spirit, but there are also gods of crops, sky, and the earth. Above all these spirits, however, is Chukwu, the supreme god. This belief in a multi-dimensional god is a source of direct conflict between the missionaries and village. Although the outcasts of the Ibo society are drawn to the inclusive tenets of Christianity, the rest of the village is put off by the idea of only one male god.
In Chapter 16, we see the first argument/counterargument presented by both parties. The missionaries argue that the Ibo gods are simply wood and stone. The villagers scoff at this notion, as anyone would whose centuries-old beliefs were challenged. Yet when the church is built in the Evil Forest, the villagers expect everyone to meet a horrible end at the wrath of the gods. When this fails to be, more villagers are won over to the Christian church.
Yes, the Ibo people worship more than one deity. For example, throughout the book it is mentioned that everyone has their own chi which is personal god that everyone has. Also towards the end we have the missionaries conversing with the Ibo people about the differences and similarities of their religion. They state that their chi are also basically messenger that gives message to the supreme. So basically the Ibo people do worship more than one deity.