No it's not! If they find a weak link, they will exploit it.
They don't line up - they hide in the backs of trucks. The Irish customs at Cork aren't prepared enough for this. Spain has millions of illegal immigrants from Africa and beyond who would use Ireland as a gateway to Britain or worse stay here.
Well, guys, no need to worry about the immigration anymore:
First of all, the ferry service will cover Rosslare / Gijon, and not Cork, and then, it won't carry any passengers as the route won't be direct between Ireland and Spain (it does a stopover in Nantes).