The key statement for here (and
another thread on baggage) is
If you will be checking in with a United codeshare partner, please contact that carrier regarding its baggage policies. ...
*A codeshares have an enhanced guidelines for *G but it is not always as generous as UA.
Non-*A codeshare may have not *G exemption.
FT Rule # 2 -- AVIOD CODESHARES -- and this is just one reason why.