Mostly, no.

They are passed down in written form with (in many cases) dots and therefore not orally transmitted.

In most cases they are fully accredited (as mentioned above).

In most cases they have not been modified by the process of transmission.

If you apply tests of form, most of them do not comply with those either.

There may be some that qualify.

Iam however also suspicious of them as having a distinct purpose but I have not really thought this through yet.

The above does not mean that there are no hymns that I like - but, and this may be a form thing mostly although content will affect me - there aren't many. My liking however does not affect whether they are folk.