hi there,
in this case, the "in whom is vested the tradition oral of the tribe" is not a clause of the sentence. it is actually a phrase constructed by "in whom is vested + something".
EX:
The corporation, which was styled "The Mayor, Sheriffs, Burgesses and Commonalty of the Town of Carrickfergus", under the provisions of the Municipal Reform Act was dissolved, and a board of municipal commissioners constituted, in whom is vested the corporate property, valued at £350 per annum.
at (http://www.lennonwylie.co.uk/PT.Cpage545.htm)
From the discussion already presented it is obvious in whom is vested title to the abandoned right of way acquired under the general grant contained in the Act of 1906 if the damages were paid and the railroad actually constructed/ at
(http://thorpe.ou.edu/sol_opinions/p501-525.html)
The other phrase can be used similarly is "in whom is trusted".
hope that help,
buzz