Such lines blur out of cultural necessity - and the singer always sings the song in their own voice. No song is ever purely (or merely) historical in that sense, neither can we allow a quest for 'authenticity' to interfere with that for a deeper humanity. How 'authentic' is the poem anyway? How 'authentic' can a poem be? It exists at several removes from the life it purports to be describing anyway. As a piece of salty-romance the poem is a nice one - but the fact remains that its essentially unsingable unless we take out the offending line, which is barely incidental to the sense of the thing.

I like the poem, I always have; I used to sing it myself 28 years back from the Bob Robert's record - replacing the offending line with a Persikonkaitas pearl-man and a blue-eyed Swede (a mouthful I admit but I was listening to a record of Persian Gulf Pearl-fishing songs at the time) although it shames me to say I allowed the Dago bunch to remain. These days I'd change that as well...