The census only asks for state of birth, but occasionally I have seen when people were born in the local county it is included. Note on the 1860 census it says everyone in the family was born in Clark Co, AL. So, I would say the parents of James were most likely married there, too. I don't know anything about the ethnic background of his mother. Did you go to the Clark Co, AL GenWeb site? Click and look, see if there is anything about Native Americans located in the county. Also, post a query on that site.
Native American blood in family lines often is incorrect. The family may have lived in Cherokee territory and that gets added to the blood lines without accuracy. So, don't be disappointed.
I went to the McAden Forum and in the Search This Forum box I typed in Clarke (for Clarke Co, AL). One lady seemed very knowledgeable about this family. On the McAden Forum if you go to the Jump to # and type in the number 2, you will find her. I looked at the book she named on the Family History Library catalog and then went looking for the Rev Hugh McAden on the Rootsweb's WorldConnect.
Type in McAden, Hugh born 1730 + or - five years and up will come about 13 matches. I just chose the one that gave full name of burial location and found lots of notes and sources. But, I suggest you click and look at some of the others, too. Birth location is given as PA and Scotland, so there is some disagreement over his birth. You are getting into Colonial Records and it gets a bit harder to do some of the tracking by then.
I would get in touch with anyone who has something on your direct line, see if they know any thing about Native American blood in the family.