Seems as good a place as any to post about my experience today flying on Vueling BRU-BCN with IB code/purchased on Iberia.com.
1) Received email from iberia.com prompting me to check-in online.
2) Able to choose exit row seat
and print off IB boarding pass with IB flight number and AA number/Emerald status on BP.
3)Dropped off bag at Vueling check-in counter and they confiscated IB online boarding pass
and gave me Vueling BP with no mention of AA/Oneworld/Sold as IB etc.
4)Didn't notice at desk that the new boarding pass had stolen my exit row seat allocation
5)IB departs Terminal A in BRU as does Vueling and IB has spacious lounge there (BA lounge is in Terminal B). There is a common registration check for 4 different lounges so the staff member may not be totally up to date with the Oneworld Lounge Access Rules based on Status ie if flight is not Oneworld-operated AA EXP status doesn't get IB lounge access.
6)Had a copy of the IB boarding pass that Vueling had pilfered from me and common lounge check-in agent happily admitted me to the IB lounge when I presented that BP and AA EXP card.
7)There was no IB-operated flight for a couple of hours and while there is a desk in the IB lounge which might be manned when there is such a flight it was not for my flight.
8)There were zero other passengers in the lounge - I would have expected some IB elites who unequivocally have right of abode in the lounge, but none.
9)Note I think this might only work with online check-in as even kiosk check-in selecting the IB flight option spits out a Vueling boarding pass.