Ok, the story about this is realy that Hergé did have to complay with the Editor of Le Petit Ving-Tieme, a vary staunch conservative and nationalistic newspaper. It was the Editor, a Catholic Priest, btw, who convinced Hergé to make Congo they way he did. Many years later Hergé redrafted Congo himself, cleaned up the Africans' (congolesian's?) speek about and substituted the national geography lesson for a math lesson. (tintin also went to soviet, and this album was also used in the Le Petit Viengtieme's propaganda against communism; later Hergé redrew (some of) this album, too.
There's another album Hergé revised. It is the one with the firestation, where the fireman have forgotten his key to the station, but I can't remember the name of the album? Sorry about that.
However, if you look at others of Hergé's works, you will see that they are very political indeed. In the Blue Lotus, Hergé speaks up for the Chinese, while the rest of the world at that time (1934 or so?) did root for the Japanese. (of course, the japanese are drawn as charicatures). In the Crab with Golden Claws, Hergé explores the smuggling of Cocaine, this related to the dangers of opium in the Blue Lotus and in Pharoh's Cigars. In the Land of Black Gold, he actually has a very interesting scene (politically speaking) in which an arm's dealer sells arms (weapons) to both parties in the war for oil. (very educational, I might add). He also has scene in which the big Oil Companies agree on dividing the oil concessions between them. Again, very educational. And in the Red Sea Sharks, he openly attacks (modern) slavery.
In Flight 714, the businessman, Rastapopolous, admits to being a scoundrel and a thief, from very early in his live. And Tintin actually supports a revolution in small Latin American Country - in Tintin and the Picaros.
And in King's Ottokar's Sceptre, Titin prevents a coup d'etat as does he in
The Calculus Affair. (and prevents the invention of a weapon that will lay wastes to building using sonic? radar? waves?).
As a more general comment, art can never be complety ripped out from or out of the (societal) context in which it was (and is) made, not now, not 80 years ago. And people critisizing Tintin might as wll be critisizing The Phantom (mort walker) or Tarzan (Edgar R. Burrows) for being colonial in their attitude towards the native's of Bengali or Africa, since it takes a white man to solve their problems. And Tintin in Congo is a sort of testament over the colonial period in Africa. And it is important to recognize this.