No. Currently, Ethereum's EVM infrastructure does not allow for private transactions in a computationally efficient and scalable way. Because of this, we have handwritten the custom ZK circuits for Polybase, enabling true privacy on a public blockchain.
Where does validation take place? Sequencer, prover, or both?
The sequencers and provers both perform some part of validation. They can both be run by the same node.
Does Polybase have public or private node operators?
For testnets we won't have external node operators. For mainnet we plan to have a few trusted private node operators. Then after mainnet we will open up the network for anyone to run a node. If you have interest in running a node, visit our section Run a node