Vueling is still a Terminal 3 based Menzies handled non Oneworld airline with no Iberia or BA flight codeshare (is that last bit right?).
From the Who handles who 2012 thread . . .
ASIG
Emirates (Pax/Despatch only)
Iberia (Pax/Despatch only)
Scandinavian Airlines
Thai Airways Int'l
Turkish Airlines
Vueling (Pax/Despatch only)
British Airways
British Airways
Iberia (Ramp only)
Vueling (Ramp only)
Not sure that Menzies do handle Vueling in LHR, but this may be old info?
GA