The Swingle Singers were originally a French group, founded in 1962, and the performance you just listened to was from 1963. The group has been in existence ever since, though now based in London and with different personnel. The current members are all either from the UK or Canada. The line-up is either seven or eight singers plus string bass and drums. They have been hugely successful in a niche they created for themselves. In addition to many awards and the use of their music in films and television shows, Luciano Berio wrote his Sinfonia with them in mind and they did the premier recording with the New York Philharmonic.
What I don't like about what they do with the Contrapunctus IX from Bach's Art of Fugue has less to do with their vocal performance than it does with the bass and drums accompaniment. True, I don't think that 'swinging' the eighth notes adds anything except superficial excitement, but that is partially offset by the nice chorale effect of the main theme in the long notes as it appears later on. This is more effective than it would be on the harpsichord, for example. But I just can't stand the bass and drums. The bass especially, as a walking jazz bass has no purpose in this kind of counterpoint and just muddies up the texture, making it harder to hear what is really going on. Also, the drums are an unnecessary added noise.
Here is a much better way to perform this Contrapunctus:
With that much going on, how could anyone think it was a good idea to add bass and drums?