It is normally not advised because danios tend to be fin nippers. That, and the fact that danios look like they have ADHD as they zoom around the tank, I wouldn't house them together unless you had a medium size community tank of 55 gallons or more. Even then you might have problems with fin nipping.
Remember that the tank your fish lives in is his or her's whole world. Ask yourself this question, and answer it honestly: would you choose to live there?