One celebrated singer I recall using an aide memoire was Peter Bellamy performing songs from "The Transports". He had a music stand for his little book too.

I guess that when Sandy Denny recorded "Tam Lin" she had the words in front of her!

Martin Carthy has been known to use a tablet (a small configurable flat screen, for the traditionalists among us).

If the above don't pass muster, even Joseph Taylor used to forget the words occasionally. Mind you he was a bailiff, not a folkie.