|Ok, this is a rather convoluted setup and there's not likely to be a lot I can do (without more intimate knowledge of your LAN) to help but I will try.|
From the sounds of it with the one router in the DMZ, both routers are connecting to the other via the internet (thus the multiple hops between....if they're communicating via the LAN, then there should only be 1 or maybe as many as 2 hops between). Are they supposed to be connected on the LAN side as well?
The other thing I'm curious about is, are the two routers doing the job they're intended to do?
If they are working properly, and they're not intended to connect via the LAN, then I fail to understand why it's even an issue that one isn't responding to a traceroute from the other. Perhaps you could explain a little more what it is you're attempting to do/ascertain by doing the traceroute between the two.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.