American old time string bands recorded in the 20s and 30s occasionally have a cellist. Cannot think of any names at the moment.

I actually know a professional cellist who plays old time music. He can bow a gorgeous bass part. He can also play melody in a pizzicato style that reminds me of a frailed/clawhammered banjo.

Cellos are not yet common at places like the Appalachian String Band Festival at Clifftop WV, but they have started to appear over the last few years.