Violas would probably have been used to play two-string rhythm lines in klezmer bands in eastern Europe. In some areas the viola players would take off the top string and shave the bridge to make it flatter, so that playing chords was easier.
Klezmer violists in the late 19th and earlier 20th centuries included:
USA Leonid Bolotin
Klezmer violists in the later 20th century and today include:
Germany Nadja Trnka
USA Cookie Segelstein (also violin), Laurence Traiger