I can't help but think that this is not a real surname. The information on this guy is that his name throughout his youth was Shammgod Mills, and that he changed it to God Shammgod, claiming that this was his father's name. There's no solid evidence of this that I can find. Shammgod seems to be one of those made-up African-American given names like Shaquille, Geroy, Latoya, and the like.