The main reason turtles carry salmonella is because as lilbug stated, salmonella is an intestinal bacteria and in captivity turtles swim in their own feces. If chameleons transmitted salmonella via kissing, Jannb would be in big trouble :p.
I made the mistake of keeping mine on paper towel substrate for a day or so. Needless to say it was gone the next day (all of it). But as Kara said, super easy, nothing to it really.
Normally the impact that the tongue has on the mantis renders them defenseless. However, if your chameleon is weak or has feeding issues I would suggest sticking to smaller mantid prey to reduce the risk of injury. Otherwise, you should have no problems as long as the mantis is of suitable size.
The black ones with yellow stripes you should stay away from (Zebra Longwing), but most species with earthy tones (the Painted Lady included as it is a brick/tan/brown) are safe. Monarchs are very easy to tell apart due to their size and iconic black abdomen with white speckles.