Really? what evidence is there that he had an impact on the French Republican/Colonial ideology. Some radical thinkers in France did attack the colonial ideology - such as Jean-Paul Sartre and Jean-Francois Lyotard, both of whom were active in solidarity with the Algerian resistance. Then there were some who went further (some would say too far) like Jean Genet over Palestine, Jacques Verges and Michel Foucault. I cannot see much evidence that Derrida did anything...
... but when you add "...and its epistemological manifestations", maybe that makes sense - if you see Republicanism and the Enlightenment tradition as leading inexorably towards colonialism. But that is itself a tendentious point, and one that does more to justify anti-rational and anti-democratic currents than it does to challenge colonialism.