the list of what all insurers must cover is here (trade body's web site, German only):
http://www.santesuisse.ch/publicatio...rsicherung.htm

however, there is nothing specific about hearing problems or aids, nor could I find anything searching my insurer's web site for some specifics. My uneducated guess is that coverage for hearing problems will vary widely from insurer to insurer, and may not be as favorable as in the UK.