Substrate COULD cause impaction. It will also hold moisture which COULD be host to lots of bacteria because it doesn't have any way to drain itself like in nature.... so.... why take the chance?
For veiled, look at this site: http://raisingkittytheveiledchameleon.blogspot.com/2007/12/supplements.html
For panther, look at this site: http://www.prismchameleons.com/Care.html