No. The Congo Free State was a private venture of King Leopold of the Belgians, it wasn't anything to do with the Belgian state or government, so Belgian troops could not be used. The lofty-sounding International African Association recruited European mercenaries to be officers and NCOs, and Africans from Somaliland, Zanzibar, Liberia and other parts of West Africa. Officially they were escorts for scientific and commercial expeditions, but they were in reality destined to be the army of Leopold's new private colony. At this time there were no uniforms.
Once the Congo Free State was founded in 1884, these troops were organised into the colony's army/police force, called the Force Publique, and local Congolese troops were recruited as well.
By 1908 the Congo Free State was embroiled in scandal over terrible mistreatment and exploitation of the natives, and the Belgian government took it over as a Belgian colony. The Force Publique remained as the colony's army.