I think we might be getting mixed up a bit here. Typically, mouth music doesn't have too many words that make sense. Puirt a Beul simply means mouth tunes and were popular in remote areas where there were few musicians or not enough of them when needed. What words there are would be used to accentuate a turn in a tune or a change in rythm.

Waulking songs, from the Outer Hebrides are very rythmical and do have verses and a lot of nonsense verse. You may have heard of waulking the cloth or "luadh" as the process is called in Scots Gaelic.

Anyway--my two cents worth.