This applied to running Edge dev or device VM's in Azure.
Azure D and E version 3 VM's support the nested virtualization that Azure IoT Edge requires. Nested virtualization support was announced last year so perhaps other version 3 or newer VM's support it too.
If you pick the wrong VM type, you can pass Edge's prerequisite validation but containers will fail to start with a message that no hypervisor is installed. At first I used a B8ms VM and encountered this problem. Luckily Azure lets you change the VM Size so I switched to the D8s_v3 size and it worked.