Hello Champion
By definition, a stub area in OSPF cannot be a backbone area. For this reason, in order to configure an OSPF stub area in the DMVPN topology, an area other than area 0 had to be used. Take a look at this lesson for more information on stub areas.
It is possible to create a multi-area OSPF design for a DMVPN topology, however, there must be a reason for it. What do I mean? Well, OSPF should be split into multiple areas in order to make OSPF update messages smaller and to minimize the number of OSPF updates that may be sent over slower links. These factors have to do both with the scale of the network as well as the architecture and topology of the network.
One approach for DMVPN is to put one or more hubs you have into the backbone area, and then assign a different area to each spoke. This is useful when you have large networks with many prefixes behind each of the spokes. Another approach is to put the hub and spoke routers into area 0 and put the LANs that exist behind each spoke into non-backbone areas.
Having said that, if you can have your whole DMVPN topology within a single OSPF area, it is preferrable, since it eliminates the complexity that a multi-area OSPF topology introduces. Unless your network is so large that OSPF begins to slow down, and updates are becoming too large, it would be best to keep everything in one area.
I hope this has been helpful!
Laz