Yes, he could have played for us. They used to call him 'Paddy' at QPR I once read in a magazine or news paper.
The Ferdinands were eligible. It's mentioned in Rio's book about an Irish grandmother.
Kevin Harper who represented Scotland was also eligible for us. As was Darren Fletcher. Paul Scholes was probably the one that really got away.
I think there may be a few American internationals that had Irish connections as well. John O'Brien (with Ajax at one point I think) may have been eligible.