Yes, NSX-T is required for any cloud/destination installation. NSX Requirements for HCX Deployments (vmware.com) - there is a helpful product interop matrix link on that page too. Without HCX cloud...
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Yes, NSX-T is required for any cloud/destination installation. NSX Requirements for HCX Deployments (vmware.com) - there is a helpful product interop matrix link on that page too. Without HCX cloud in your on-prem I don't see a way to extend subnets to it via HCX. There are other ways to stretch/extend subnets but they are not as easy to implement.