Part of what makes a song acceptable by the Folk World is the way it is treated ! IF any composed contemporary song CAN be classified as Folk (Which I find personally a VERY reasonable suggestion) The way it is performed will make a world of difference ! A lot of Pop and Rock numbers work perfectly well as acoustic Ballads (Ballad in the MODERN Context , of course) - Buddy Holly , the Beatles , Beach Boys ,
even the Rolling Stones are all acts whose songs I have heard done in Folk Settings without any clash !
Clifford T Ward was never , and never COULD be called Traditional , but that does NOT immediately bar his songs from performance by 'folk' artists .