Hello Rcscullado
It is possible to create a DMVPN topology where you have spoke routers assigned to different BGP AS’es. You can use the neighbor peer-group remote-as multiple times with different peer groups referencing different routers, and each one in a different AS.
This configuration is fine if you have two, or five or even 10 spokes, but what if you have 500? It’s not that scalable. So in general, the rule of thumb for larger networks is to either use iBGP across all of your DMVPN topology with a single AS, or use eBGP with the hub in one AS, and all the spokes in another AS, just like in the lesson.
You can group your spokes so that each group corresponds to a single AS, but the benefits of this may be somewhat limited. The groupings must have some characteristic in common, such as belonging to a particular city, or department, or company, so that this grouping and the resulting routing can have more meaning and usefulness.
I hope this has been helpful!
Laz