Involvement in politics has not been a reason to deny sainthood.
As King Henry's remarked about St Thomas a Becket, "Will no one rid me of this troublesome Priest?”
We don't know what his stand was on conciliarism, or even if he had a stand. He probably was too engrossed in events in his parish in Poland to go into the topic, unlike we armchair theorists, who have the luxury of opining.
I'd like to find out more about him before I would doubt Bl. Jerzy's eligibility for canonisation..