Every government on the planet has some corruption. Any claim to the contrary is in denial of true human nature. Man is greedy. It has been this greed that has created man's survivability. Those that were the greediest survived, and greed is now inherited. Government officials are no different. Particularly high level government officials are susceptible to this greed considering their level of influence. The Kremlin does have corruption.
As more and more FOIA documents are released, the extent of our own governments corruption becomes clear. We have a strong constitution, a strong free press, and still have corruption issues. If you look at the Kremlin, with no freedom of press, no guaranteed rights, it would be absurd to think that they were not corrupt.
Yes, the Kremlin is corrupt, because they still exercise more or less complete control over Russia and its citizens. Remember, this is the country that still imprisons dissidents. Every aspect of a foreigner's visit to Russia is carefully controlled. The Kremlin will do anything to maintain their stronghold of power.
The Kremlin is simply the city center of Moscow and the building contained within that area. They are buildings, they can not be corrupted. Do corrupt things happen there, it is possible, but that doesn't make the Kremlin itself corrupt. Terminology is pretty important, have you had an issue with other buildings being corrupt?