The xylophone has not been used very much in klezmer. Perhaps the best-known player was Jacob Hoffman, who left Ukraine and settled in West Philadelphia in the 1920s, leading klezmer bands and playing xylophone and drums in Harry Kandel's Orchestra, as well as playing with classical orchestras.
He had klezmer yikhes (lineage) as his father Joseph was a klezmer, and this continued as his daughter Elaine became a klezmer drummer, and his granddaughter, Susan, a klezmer trumpet player.
Michal Josef Gusikov was a virtuoso player of a xylophone-like instrument who toured Europe in the 19th century playing Jewish themes with variations, along with other more classical repertoire.
Klezmer xylophone players in the late 19th and earlier 20th centuries included:
USA Jacob Hoffman (also drums)
Klezmer xylophone players in the later 20th century and today include:
Germany Alex Jacobowitz