While Alex and Rolf were visiting, I pointed out that the Dolphin card was not sending any data, not even a time stamp, from the c1lsc machine.
After some poking around, we realized the IOP (input/output processor) was coming up before the Dolphin driver had even finished loading.
We uncommented the line
in the /diskless/root/etc/rc.local file on the frame builder. This waits until the dolphin module is fully loaded, so it can hand off a correct pointer to the memory location that the Dolphin card reads and writes to. Previously, the IOP had been receiving a bad pointer since the Dolphin driver had not finished loading.
So now the c1lsc machine can communicate with c1sus via Dolphin and from there the rest of the network via the traditional Ge Fanuc RFM.