Unlike some other FF alliances, in *A, and with UA, crediting is done based on operating carrier only. If the operating carrier isn’t a UA partner for earning, then you won’t get miles, even if UA tickets these flights. There are lots of situations where UA will sell flights on airlines that aren’t FF partners (usually, connecting to a long-haul UA flight) and you will only earn on the UA flights. As already mentioned, HK Airlines is one, but I’ve also seen CX, Jetstar, Jet Airways and more. In at least some cases, you can’t even check in to the UA flight if starting with the partner.