Did you ever get a config that worked ? I am trying to use a pair of ISR 4431 as hubs and 100+ RUTX9 as spokes. The sample configs Ive seen, seems to be for lab only (WAN on same subnet) so I am not sure the NHRP would work in real world, behind double NAT, carrier networks etc.
I always seem to get IKE P2 failure - although I haven't yet done any deep diagnosis.
In my setup the spoke can ping the hub tunnel source IP however the spoke IP is not directly available to the hub. Thats should be where NHRP comes in.
I am very familiar with DMVPN (Cisco to Cisco) as we currently operate 600+ site network.
Any thoughts would be appreciated.