I think you are right about them being Germanized versions of originally Polish or Slavonic names.  I've noticed that German names ending in "ke" frequently have a history in the eastern areas of the former empire, i.e., East Prussia, Silesia, Pomerania etc.

In Czech, a related language, "ka" is often a diminutive form of feminine names and nouns. 

As for Pollack, it is more obvious. "Polak" means "Pole" i.e., someone from Poland, from "pole" field, from the "land of fields." Then there are various variations in spelling like Pollak, Pollack, Polak, Polack, etc. "Pollock" might even be an anglicized version of the name.

There can be non-Jewish Polaks, for example here in Bohemia where I live. However, I've never known a Gentile "Pollak". They may exist, but I've never encountered one.

Rick Pinard, Prague, Czech Republic