I think I'm right in saying that all BA do when checking with a partner airine is to confirm:
(1) that you actually flew that sector on the date shown
(2) that you were ticketed in fare bucket 'X'
(3) that you had attached your BAEC number to the PNR
So their system would probably be blind to the fact that UL was denying miles to their own members, and any manual intervention would most likely follow the steps above.
I assume one would therefore have a reasonably defensible position, as I-class UL fares are shown in the BA calculator as earning 140TPs per sector on those routes.,. but I agree that it would rather gutwrenching to have 560, 1120 or even 1680 TPs relying on that assumption, especially if BA started to play silly burgers !