Are Victor and Junior the same person?

Victor and Junior are friends. They are not the same person. 

Victor Joseph

The main protagonist in the collection. He appears in many of the stories and grows from an innocent child to a disillusioned young adult. He endures poverty and racism as a child, and makes a difficult transition when he attends high school off the reservation. As an adult, he has several unhealthy relationships with white women and struggles with alcoholism, but with great effort he eventually stops drinking.

Junior Polatkin

One of Victor's friends. Junior is one of only a few Indians on the reservation to attend college, and because of this, he has a tense relationship with his peers. He attends Gonzaga University and fathers a son named Sean with a woman he meets there, although they break up shortly after his birth. Junior drops out of college and returns to the reservation, where he faces alcoholism and poverty.

 Victor never left the reservation or went to college?

From the text above:

He endures poverty and racism as a child, and makes a difficult transition when he attends high school off the reservation.