Green’s Dictionary of Slang

Uncle Tomahawk n.

[play on Uncle Tom n. + SE tomahawk, the trad. ‘Red Indian’ weapon]

(US) a Native American who is condemned as insufficiently nationalistic.

[US]E.E. Landy Underground Dict. (1972).
[US]N.Y. Times Mag. 13 Feb. 46: If the tribal constitution permitted it, he would prefer to remain in office rather than join the wandering bureaucrats some call Uncle Tomahawks.