Yes, but you can verify blocks independently and see that someone verified a block that was actually invalid. It's not something that can remain secret.
But you won't verify the blockchain and call every node to say "hey! big corp X is cheating". The consensus protocol is what it is and if 51% agree on anything it will go on. We are at the mercy of 4 giants messing with the chain. Also probably simple double spending could be noticed and proven wrong but, for instance, rolling back a transaction would still be possible breaking the immutability of the blockchain.