G187986-002 for Fibre Channel SPF+ modules?

Onwards on my quest to get my LTO drive working, I now have an external Thunderbolt 3 connected G18786-022 card for two SFP+ modules that identifies itself as "DM7801BJ" from "Shenzhen Dongman Technology Co.,ltd". The Thunderbolt part (of which I assume the above identification comes from) is connected via M.2 to the (Intel? Dell?) PCB. Now, when I put in two Fibre Channel SFP+ modules and connect one with the other, the (apparent) Link LED lights up on both sides, yet my Mac sees no Fibre Channel devices ( I would assume there is none, as there's no "slave" devices connected?). Connecting either of my SFP+ FC modules to the LTO drive - no light.

Any idea if
a) the card is actually capable of supporting Fibre Channel (the reseller says yes);
b) there's any FC troubleshooting guides/apps for the Mac (check link layer, check SFP+ comms etc.)?