With my Quadra 630 attached, (needed to run NetBSD) I have gotten much further with the ethernet support. The Cabletron diagnostics now recognize the device. Likely just due to the incomplete Mode Sense implementation, NetBSD and its related tools don't like my disk emulation. And on the unforeseen complications, I now have to put some form of mutex / locking on the ethernet and oled drivers, which pushes me closer to switching to an RTOS and changing how I handle the SCSI PHY.
UPDATE: I just suck at installing crusty drivers. The Cabletron MacOS driver isn't an extension like you would expect, instead it patches the System file with the actual driver, and has some sort of patched Ethertalk extension. I'm further along than before, but without having the original hardware to compare against, I'm just blindly implementing their protocols by reading the NetBSD driver source code. The driver goes through the process of adding a protocol and a multicast address to the frame filter, and asking for any available frames. If the stats DA is installed, it attempts to poll as well. I suspect the card returns some sort of "No data, ask later" response when there are no frames to retrieve, but can't find any reference in the NetBSD driver.