Hi Ricardo,
The difference between OSPF P2MP and broadcast/non-broadcast is that with P2MP, the next hop will always be the hub and with broadcast/non-broadcast it will be the remote spoke. I have an example for this:
This is about frame-relay but it’s the exact same thing with DMVPN. If it’s working with broadcast (where the next hop is the remote spoke, not the hub) then it indeed sounds like an issue with the next hop override.
You could try to enable some NHRP and OSPF SPF debugs on your routers, see if anything happens. Is there a reason why you want to use OSPF? Since it’s a link-state routing protocol, it’s not the best option for DMVPN. All your routers are in the same area so any change triggers an SPF calculation.
If broadcast works then I don’t see a problem to use that instead of P2MP.
Rene