Native VMC segments have access to AWS Linked VPC via the xVPC network.

There is no need of a VPN to achieve that.

However, when you stretch a network from On-prem to Cloud, using HCX or NSX L2VPN client, the gateway IP remains at On-prem.

So for any VM on this stretched network to talk to anything outside its own network, the traffic will flow back to On-Premises and in order to reach an AWS VPC, you would need to create a VPN or DX link. This routing needs to be configured at your On-Premises