I believe the way it works down here, is that if a home game isn't sold out, the local networks will black out the game. I know it's the case with the Raiders, but I can't remember it happening with the Niners (maybe they sell out all their games?). I would guess that anything blacked out in Seattle would also be blacked out in Spokane, but that's just a guess.
This is accurate. Not sure about Spokane though... when I lived in LA, we never had games blacked out (as we had no assigned home team). However, we never got consistent coverage with games, as... we had no assigned home team. We did get to watch the best matchups each week though.
And Ken is correct, the Niners sell out every home game, whereas the Raiders don't. Though I think this has more to do with the fact that Al Davis built Mt Davis on the top of the Colloseum, this guaranteeing he will never sell out, and also that he charges insane prices for Raider tickets.