> is this any conceptually different from using PKCS11 provider for TPM in OpenSSL?

PKCS11 doesn't allow you to attest that the key is resident in the PKCS11 provider, which as you say, the author alludes to, but doesn't cover.

> with real TPM, the key could be locked to a specific configuration register value, which makes less sense for VMs.

A vTPM is as real as a physical TPM chip.

The question is which TPM endorsement certificate CAs you are willing to trust.

For some that might the manufacturer of TPM chips, for others it might be their VM provider. (For some, none: for some both!)

Trusting their VM provider isn't so crazy if the VM provider is able to influence the guest code anyway.