The concentrator does support one-armed tunnelling, no problem. Use the Private interface of the concentrator for this rather than the Public. This doesn't work for LAN-to-LAN tunnels (only remote VPN clients), you also lose IPsec over TCP and load-balancing features. Not a recommended solution but certainly does work.
You couldn't really connect up both interfaces to a single DMZ cause that would imply both interfaces have to be in the same subnet, which is not supported.