Qemu is the hypervisor in this situation. Which doesn't necessarily preclude having Rosetta acceleration of AMD64 binaries within the ARM64 Linux guest itself.

That said, as far as I know, the only official way to use Rosetta inside a Linux guest is using Virtualization.Framework, which allows mounting a Rosetta binfmt handler via Virtiofs. So it's also going to use Qemu inside the VM to handle running amd64 images, not Rosetta.