No, Polish can't crusade at all... chapterhouse can't be built, and even if you capture one, there are no units listed with Polish that are normally part of a crusade (knights templar, teutonic knights, etc)

easy to mod, though.

just add Polish to the chapter house in the Building file, and then Polish to Crusade under the Unit file and then to a few of the Crusader units (I tend to copy the HRE ones as they are neighbors)