You can perfectly have 2 DMVPN and allowing failover using the routing protocol, plus having a dual hub configuration, but you do not have to have 4 interfaces per spoke, as you can set up multiple NHS entry (the hub) in the tunnel interface.
However, you need to have IP Connectivity between the hub as in a dual hub topology each hub is referring the other hub as a NHS so that if it fail he can still lookup the spoke using the mapping from the other hub.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...