Asiana Club - transferring from Southwest to Asiana (sfo-rep)

Is 90 minutes enough time to arrive via Southwest, check baggage and traverse security?

Too tight, in my opinion. It takes time to pick up your luggage after arrival, terminal change, and going through another security. There are later flights to ICN (SQ and UA) if you can take. Or take any legacy airlines - they do baggage interline with Asiana, and 90 minutes will be fine if that's the case.

What is the procedure for notifying Delta that you are traveling forward but not on their airline/alliance?
Also, I see you have a Seoul reference, you must have made this flight before-what terminal does it leave from and if you know its relationship to Delta's terminal.
Thanks

When you check in with Delta (or any airline except southwest, virgin america, or jetblue), say to an agent that you'll transfer to an Asiana flight at SFO. As long as you have enough time in between, they will check your bags all the way to Seoul, so you don't have to pick them up at SFO. That's a huge time-saving. You still need to go Asiana counter at SFO for checking in. In terms of terminal, Asiana uses different one, so even with star alliance, there's no advantage.

Thanks. Any lounge access in the Asiana terminal-flying bus/first

Sure, OZ contracted a lounge access in SFO for C class passengers. I don't know which one it is but you'll figure it out on their website. OZ doesn't operate F class to SFO.

When checking in with DL, you should show them the itinerary for your OZ flights. Don't just tell them you have a connecting flight, you should show them a printout (with the ticket number). If you can't print it, showing them your reservation on a phone or laptop will work as well.

If problems do arise, they would probably be for the last segment ICN-REP, so if you can get DL to at least tag the bags to ICN, you can tell OZ in SFO (or ICN) about your bag.

I have been in your exact situation before, and just, beware of the differences in luggage limits between DL and OZ, because back before I had *G, I had checked in 3 32kg bags when checking in with DL, and before OZ issued me a boarding pass in SFO, they checked my bag weights and charged me for an extra bag, and being overweight.

About the lounge, I think (Its been a few years since I flew OZ out of SFO), they use the UA lounge. But being *A you can visit the better SQ lounge