Hello Jason
cEdge and vEdge devices are inherently different. cEdge devices are Cisco-based ISRs or ASRs while vEdge devices are purpose-built SD-WAN devices developed by Viptela (the company Cisco acquired that had SD-WAN solutions). So unavoidably, the method of implementation, syntax, and commands, will be somewhat different. For a more comprehensive outline of the differences between these two devices, take a look at this NetworkLessons note on the topic of vEdge vs cEdge.
Since the syntax is different the way that the VPN0 (underlay network) is configured is also different. On a vEdge we do indeed use the vpn command, and under that command, we reference the interface that will be used as well as the route to the next hop.
On a cEdge device, we actually do this by first configuring the interfaces, and then, under the sdwan configuration mode, we reference the interfaces and then create tunnel interfaces. This conforms more to the configuration you would expect on a Cisco device with the creation of tunnel interfaces.
So it’s all about the creation of the tunnels. In one case you use the vpn command and configuration mode, in the other you use the sdwan configuration mode. In both cases, tunnels are created which correspond to the VPN 0 underlay network.
I hope this has been helpful!
Laz