Speedfusion over MPLS - DNS settings on WAN interface

I have an MPLS network and an Internet connection at 77 remote locations and at my head end locations. I want to create a speedfusion tunnel across my MPLS and Internet connections. When I setup the WAN interface at the head end that is connected to the MPLS router, I am asked to include a DNS server. Can I just include a random address for this or does that connection actually need a DNS server to work? I was hoping that the speedfusion tunnel would just route WAN to WAN across the MPLS network with no need for DNS?

FYI This is the setup I am looking to do.

If the WAN doesn’t serve for the purpose of internet surfing, you may put a random address.