Originally Posted by supine

1) UA won't touch your OZ booking

2) you can try with OZ at SFO but I'd be surprised if this works

I'd put my bet on the transfer counter at ICN being able to do the document check and issue the boarding pass.

Worst case you have enough time to exit landside.

Originally Posted by oliver2002

Ask UA in IAD, but expect nothing. Once you land in ICN, just go to the OZ transfer desk on arrival and get you boarding pass for the next flight. Since you have 4h in ICN you should be fine. No need to enter Korea.