Thank you for your reply. All external offices are cisco 3800 or 3900 routers.Everything is Cisco.
The advantage of OTV is that both DC's utilise the same subnets, mirrored. This makes vmotion between DC's seamless as the machine you vmotion across does not need to change ip address, the OTV layer between the DC's handles the duplicate ip address problem.
The issue is the DC end routers / ASA's will have different peer addresses but the same internal subnets in the match lists and advertised through ospf, I will need to read up on DVTI-SVTI or SVTI-SVTI as i haven't come across this. DMVPN is for fully meshed? These are hub and spoke but think of the DC's as Dual Hub.