What social impact did Jacob Riis have? If any impacts on America at all?

It is hard to say that Riis in particular had any social impact.  However, Riis and others like him certainly had an impact on their time.

Riis was one of the muckrakers, the people who exposed poor conditions in various aspects of American life.  In Riis's case, he made the public and powerful people more aware of the harsh conditions in which poor people in the cities lived.  The attention that this brought helped to cause the Progressives to reform the way things were done in American cities.  The Progressives pushed for better, more honest city governments and better laws to ensure that housing was safe, clean, etc.

So in that way, you can say that Riis had an impact.