The kombucha scoby uses camellia sinesis, so this means black, green, oolong, or white tea is recommended as the base for the primary ferment. Many people will add a blend of herbs, flowers, spices, etc in primary or secondary; though there seems to be a short list of what does not impact scoby development. Oils tend to cause mold development. You can read about the analysis of KT here, and there is info about what the tea provides... http://happyherbalist.com/analysis_of_kombucha.htm
Can a KT scoby be adapted to ferment other things? Definitely. I ferment coffee instead of tea, even grows a new scoby which I keep strictly for coffee ferments. The scoby is not as thick and dense as a tea scoby, but it works.