I know this is an old post, so my apologies on the revival. But I wanted to say, THANK YOU @k2x8! I've been searching off and on for weeks trying to find an answer as to why UNRAID couldn't/wouldn't show the interfaces for my Intel 10G 2P X520. I knew the card worked since I could pass it through to VM's with no issues. It was just UNRAID that couldn't use it. I'd tried all the modules I had lying around (Dell, Cisco, UniFi, Axiom, 10GTek).
After adding "ixgbe.allow_unsupported_sfp=1,1,1" to the syslinux configuration, I am now able to run utilize 10Gb.
Thank you again for not giving up and posting your answer once found!