Kris, any luck with this?
Too much going on to put time into this. I've returned my adapter.
However, I believe it is insufficient to disable the boot ROM, as the card doesn't work in Hackintoshes either, as documented here:
http://www.insanelymac.com/forum/topic/330614-10-gbe-native-support-in-high-sierra-10132/
It's also entirely possible that the iMac Pro ships with a different version of the Aquantia kernel extension. Looking forward to 10.13.3...