Pretty sure the masking is correct. I have tried allowing all initiators to see the LUN as well as restricting it to the WWN of the ESXi card. Nothing both times.
After some more searching and reading, it appears that I can't just connect the 2 boxes directly to one another. I have to go through a switch.
Just won a Silkworm 200e from eBay, should be here Fri. I'll see what happens then.