Most of the songs listed above appear to be hymns - which I know overlaps the general category of Folk - but it's difficult to determine what is Folk and what is not.

In my Unitarian Universalist church we sing hymns that were composed by classical composers (or at least the music), but the majority are spirituals, or songs like 'Tis A Gift To Be Simple (words by Joseph Bracket) - and is that Folk?

I'm no expert in traditional Christian hymns because Unitarian Universalism embraces the spirituality of many wonderful and diverse faiths, so that Christianity is only part of our energy, but When looking at Christmas Carols - many of them appear to be Folk. It Silent Night? Written by a priest (not a professional lyricist). As for the contributions of Unitarian's to Chirstmas: Once in Royal David's City, I Heard the Bells On Christmas Day, and It Came Upon a Midnight Clear: Two of those were written by Unitarian Ministers, the middle one, but Longfellow.

I would argue that much of what we in our church sing that is from the hymnal is Folk to some extent. On top of that, we supplement the hymnal with many, many other songs including Folk songs from the U.S. and around the world. We recently had a service led by members of our church who are native South Africans and they had us singing in English, Afrikkan (sp?) and Zulu.

For years, I've used Mudcat as a resource for songs for the occasional service I lead at my church or other UU churches throughout Florida.