I would not worry about this. The Alaska Airlines staff are lovely and they've been in oneworld long enough now to know the rules. I really wouldn't worry. I've flown through SEA from HNL and was able to use the Alaska Lounge without any hassles whatsoever. As someone else said, use the AS lounge in the North Satellite, it's the nicest one - if you have time. There is a transit train between all the terminals at SEA, which is quite convenient.

Alaska is a great airline (much better than AA), so you will have a good flight. If you can use Avios or pay for F, they're even better - great food, I had a glorious meal on HNL-SEA with them. On board service is always friendly too. I'm a bit of a fan and would take them over AA any day of the week and twice on Sunday given the choice. You'll be in good hands.