At least half my trips are on AS flights with a connection to AA (EAT-SEA on QX; SEA-DFW on AA, EAT-SEA-ORD on AS, ORD-PHL on AA for example.) I have never had a problem getting all of my boarding passes, AS and AA, when I check in at the airport. I can't do OLCI with mixed flights, but never a problem at the airport, whether or not they're codeshare flights, and it doesn't matter if I bought the tickets from alaskaair.com, aa.com, orbitz.com, cheaptickets.com, or anywhere else.