That configuration is supported as @Dennis mentioned and I tried that. There are two serial ports available on every Duro. In our case, on one of the ROVER Duros, one serial I/O goes to Freewave radio (to communicate with base), the second serial I/O goes to the other Duro which will provide baseline information (heading of vehicle).
White it is physically supported, I was not able to get both Position (RTK) and heading simultaneously and from just one of ROVER Duros. My initial goal was to connect a computer to one of ROVER DUROs and read both heading and position from that. However, its not supported. The (available) ROS drivers, in specific, cannot tell you about these two information simultaneously when you run the node on one DURO. As it needs to read position from one DURO and heading from the other DURO, it requires you to connect both ROVER DUROs to the computer and run separate nodes to have both information (which is not a good idea!) OR you develop your own software solution to access both data.