Can blockchain and machine learning be combined?

That is a possibility or maybe it is already happening.

For example there are the also called “smart contracts” that run on the Ethereum blockchain. Once that you send some ETH coins to these contracts there is nothing that will move those coins from there. Only the smart contracts will decide based on how they are programmed to move the coins.

Now, the programming of a smart contract may be a simple serie of instructions but it may also be a more complex algorithm for example an algorithm of machine learning that based on data learns to be autonomous in managing transactions.

So yes theoretically they can be perfectly combined at least for the Ethereum blockchain.