I was in Gladbeck for New Year's Eve 2007/2008 with my wife and we saw guest list for New Year's Eve ball, where many of guests on list had Polish surnames (more than I imagine one would see from any sample of list of German people). I did some reading later and saw that some relatively known people from Ruhr District have some Polish origins.

I wonder if you know Vedmak, do many of this people with Polish roots still speak Polish?

In the 19th century there were Polish schools, churches etc. but all that stayed assimilated themselves, so today they no longer speak Polish; I, however, read they influenced the Ruhr area dialect by introducing Polish words (also cuisine and cloths.)