Is there concrete evidence to support the notion that ethnicity is frequently a ruse for economic control by the elite?
Yes, I believe there is ample concrete evidence for this notion, and it is an excellent question, I might add.
I think you only need to look at the example of colonial Rwanda in the 19th and 20th centuries. Germany, and later Belgium, cited the results of ethnic "studies" they had conducted which divided Rwandan society into Hutus and Tutsis, and assigned authority and prestige to the smaller group, the Tutsis. This false ethnic division and unjust empowerment led to deep resentment and tension within the country and directly contributed to the Rwandan genocide of 1994.
This type of indirect rule was also practiced by the colonial British, who empowered the minority tribes in order to maintain their own control over their colonies in Africa and the resource benefits they enjoyed from them.
For further evidence, one can look at Josef Stalin's reign in the USSR from 1924 - 1953. The Soviet Union was Russia and 14 other smaller nations, and Stalin, himself a minority Georgian, brutally re-engineered the populations of these states through deportation and starvation, all to foster consolidated control by the Soviet state over its peoples.