I'll answer my own question. I say yes in either case.
If Nebraska wins on the road against Oregon, that would indicate that the team is legit. Whether they should look at upcoming games or not, some voters do, and I think they'll see a pretty clear path to 5-0 with a home game against Wisconsin on the horizon and that will encourage voters to put Nebraska in the top 25.
If Oregon wins, especially at or over the point spread, I think they'll also move in.
Of course, what happens to other teams matters, but I think the season is early enough and the game is enough of a name-game, that voters will take notice.