Just got this answer from Josef Rosin
you can't imagine any Lithuanian Jew touching pig bristles if according to any Rabi it was Taref. There were in Lithuania many Jews who dealt with the bristles or by trading with them or processing them. The Jewish workshops employed to my best knowledge mostly Jewish workers and the working conditions and the salary was very poor. I think that in Vilkavisk even a strike was initiated by the Bund- the anti-Zionist workers movement."