So the Tx from Kraken (in the mempool) is considered unconfirmed, and because it is in the mempool, it's ok to spend the utxo of this tx in another Tx?
Yes. You can spend unconfirmed outputs.
Just note that you can't get confirmation for the child as long as the parent hasn't been confirmed. (It's possible that both transactions are included in the same block).
Is it common to see this pattern in the blockchain?
Yes, you can see many of them in the blockchain.