Bromber Bloody Sunday was indeed instrumental in this action, as without this very vital and important incident, the killing of poles most certainly would not have been agitated and carried out in such a fashion that has led this to be considered one of histories most horrific and bloody tragedies.
Yes, I think it's pretty well proven now that the Bromberg Bloody Sunday was instrumental in the later killing of Poles. When a town gets together with torches and pitchforks to murder an entire ethnic minority because a government they did not belong to or support invaded, it has to pay the price.
The Bromberg Bloody Sunday killings of minority ethnic-Germans by Poles directly led to reprisal killings of Poles by the Germans. Between 80 and 100 Poles were later executed by German forces on charges of participating in the massacre. A great many more were most likely killed indirectly due to Bloody Sunday, as the German military was particularly heavy handed on the Polish population of Bromberg (Bydgoszcz) for the duration of the occupation.
Yes, I think that Bromberg Bloody Sunday was instrumental in the killing of the Poles, just like Kristalnacht was instrumental in the eventual genocide of the Jews. As each act of violence occurs, and it is not responded to, the public sees it as the governing condoning the action, and they will escalate.
No, I do not think that Bloody Sunday had anything to do with the later killing of Poles. The Bloody Sunday incident was, in my opinion, a completely separate event, and when the Nazi's killed the Poles it was not pushed forward in any way by the events at bloody sunday.