Whilst the vast majority of these chorus vocables are just that, and can be found in all genres of music, a notable few can be traced back to meaningful statements. Check out the 'rigdum' threads for instance. The long string of seeming nonsense that occurs in some versions of 'Froggy' can be traced back to early eighteenth century camp-followers cant.
Some like 'derry down' are so old and ubiquitous that we will probably never know if they had a meaning.