Yes, you're correct on both, though I think Google Cloud recently started supporting it as well. AWS will likely have GPU enclave support with Trainium 2 soon (AFAIK, that feature is not publicly offered yet but could be wrong).

We work with Edgeless Systems who manages the GPU enclave on Azure that we speak to from our AWS Nitro instance. While not ideal, the power of enclaves and the attestation verification process, we at least know that we're not leaking privacy by going with a third party GPU enclave provider.