Great question!

The thesis you're asking about is an example of the historical-materialist (Marxist) critique of slavery and racial oppression, of which Robin Blackburn is probably the best known and respected scholar. This school of thought holds that class (rather than race, gender, religion, &c.) is considered to be society's 'primary contradiction' from which all these other forms of domination arise.

Here, the idea is that in order to suppress the proletariat and prevent them from uniting in accordance with Marxist orthodoxy, the ruling, aristocratic class engineered divisions among the working class along racial lines. Now, in order to make orthodox Marxism 'work', race cannot be the 'primary contradiction', it must be a superstructure engendered by class society.

The example you've brought up is a tricky one, because race is a construct rather than a biological reality. However, I disagree with several aspects of this thesis. A major criticism of Blackburn and the Marxist critique of New World slavery is that slavery - and racial oppression / domination - existed long before the modern period. Another is that the economic habitat most hospitable to the Atlantic slave trade & plantation slavery was not laissez-faire capitalism (which actually precipitated the trade's decline), but physiocratic mercantilism. (This is a case of Marxist historical materialism working against orthodox Marxist teleology.)

Finally - and most controversially - there's the problem of malicious intent and conspiracy. For white aristocrats to have 'invented' racial domination in order to maintain their class privilege, they would have to have 'seen' and purposefully chosen white supremacy to that end. Not even Blackburn has been able to produce convincing evidence that this was the case.

Is it true that the New World aristocracy benefited materially from white supremacy? Absolutely. Did they invent white supremacy for the purpose of maintaining class privilege? Not so likely. White supremacy as a power structure and white privilege as its dividend had existed for a long, long time before plantation slavery in the Americas.

Here's a review of Blackburn's major work along these lines, The Making of New World Slavery : from the Baroque to the modern. 1492-1800 which elaborates on some of the issues I've mentioned.

See also : Charles W Mills, From Class to Race : essays in white Marxism and black radicalism. Lanham : Rowman & Littlefield, 2003.

Also, I very much recommend a look at Cedric J Robinson, Black Marxism : the making of the black radical tradition. London : BDC, 1983.