In the audio there seems to be an added vowel after faireachdainn, could be epenthetic?
No, I think there is just an artificial pause between words for clearer pronunciation aimed at learners.
I don’t really hear a true vowel (an additional syllable) if I listen to this entry in the Marsaili vocab entry and I don’t think you’d hear one in a regular fast speech.
That's a relief! Tapadh leat a charaid!