Nonsense syllables, or vocables, of this sort are extremely common in Irish, English and Scottish traditional song, and probably have nothing at all to do with languages being disapproved of!  Of course it's perfectly possible that -in Ireland, at any rate- they may sometimes be fragments of garbled Gaelic, but Gaelic-speakers also use them a lot (the "hi ri hu o" type of refrain so much used in the Western Isles of Scotland for example) and it's also worth mentioning that French traditional song has plenty of equivalents: "ma tan dé: ri-tou-dé-ra-la-la-la" comes to mind.  I strongly suspect that almost all singing traditions use this sort of thing.  The practice of singing dance music - often to meaningless vocables- when instruments are not available is very old; perhaps it is a carry-over from that.  There are people around here who know a lot more about that subject than I do.

Malcolm