Does a non-immunized baby in the daycare pose a risk to my child?

Potentially. As long as we have international air travel and illegal immigration, we are exposed occasionally to vaccine preventable diseases. At the market, eating out, at school, they can bring it to your community and not have symptoms. Any unimmunized kid is at high risk to get and pass these diseases. I never let them in my practice for 30+ years and encourage parents to avoid them.
Unknown. Depends on whether the "non-immunized" child succumbs to disease and how resistant your child is to that disease.