Guitar
Andreas Schmitges by S. Pachonik
Guitars tended to come with mandolins in groups of Jewish musicians in eastern Europe, not in the older or Jewish bigger wedding bands which were (at least initially) dominated by bowed strings. According to klezmologist Michael Alpert, in former times the long-necked fretted instruments (guitars, lutes, ouds) were more the preserve of Romani musicians.
It's also possibly that the acoustic guitar's lack of volume compared to other instruments counted against it - violins & violas playing rhythm would probably be heard better.
Klezmer guitarists in the later 20th century and today include:
Australia David Krycer
Germany Andreas Schmitges (also mandolin), Frederic Zahn
UK Matt Bacon
USA Avi Fox-Rosen (also banjo), Jeff Warschauer (also mandolin), Nick Millevoi, Pete Rushefsky (also tsimbl, banjo), Yoshie Fruchter
South Fallsburg Bulgar by Dave Tarras played by Dan Blacksberg and Nick Millevoi
The guitar as accompanist in a modern klezmer recording
Baym Rebns Sude played by Jeff Warschauer
A version of S'iz Nito Keyn Nekhtn (No More Yesterdays) performed by Deborah Strauss (violin) and Jeff Warschauer (guitar)
Krakow Jewish Culture Festival, 2014