What Possible Pronunciations of 也 exist in Suzhou Dialect?
Zhang Jiqing singing Kunqu, always a pleasure to listen to.  

The 也 here is the sentence final particle.  It's used quite differently in vernacular literature in the Ming-Qing than it is in classical literature, where it's almost like a copula. The references from 漢語大辭典 are talking about the use of 也 as a loan character for 匜, which is pronounced yi.  This is common in bronze inscriptions ca. 500 BC or earlier, and has nothing to do with the 也 here.

As for pronunciation, after listening to the 2 examples several times, I'd have to say that it's still diphthongized, just like in standard Mandarin. The Kunqu pronunciation is not actually Suzhou 土話. It's like the pronunciation in Peking opera, in the sense that it preserves older facets of Mandarin, but has a definite southern flavor to it. One part of this flavor is that a number of diphthongs are much less like two vowels and are more like a single vowel with a coda, so that the -e coming after i- is less conspicuous; this is strengthened by the fact that its a sentence final particle.  Anyway, I'm sure that its a 也 in these two places. The subtitles are accurate, just copied from the libretto.