Sheb Wooley was also one of the bad guys in 'High Noon'
Johnny Cash did several dramatic turns on TV in TV westerns in their day. And, later, 'Little Houses on the Prairie' and TV movies.
Merle Travis was an NCO in 'From Here to Eternity'.
Tennessee Ernie was in 'Best Years of Our Lives' (well really only as a singer), and, sans mustache, a Randolph Scott oater.
Dick Haymes did lots of 20th musicals in the '40s.
Johnny Johnston, a band singer of the 40s, wanting to become a dramatic actor, passed on singing the title song to 'Unchained' in which he was a co-star. Bad career move!   Everyone except him has had a hit with 'Unchained Melody', and his dramatic career ended there too.