A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,413
AFAIK the normal *A rule that the metal matters and you must translate the fare class for codeshares would apply here. So you should earn according to the UA chart for A3 miles on the A3 website, but at whatever UA fare class is equivalent to the US fare class of A.
What would be the cost difference to book it as fare class A on UA? Then the miles would be unambiguous and generous.