The white part of the feces is actually the reptiles equal to urine. Should not really be to harmful in terms of bacterial growth as it is mainly composed of potassium, sodium, chloride and ammonium salts. No living stuff really finds ammonium that appealing. When your veiled gets older you may notice that he has white build up around the insides of his nostrils. This is the same composition as what is coming out the other end. Veileds among a couple other reptiles have evolved nasal salt glands. This helps them to conserve water by excrete these toxic substances out of their nose rather then wasting water with urea.
As for cleaning. Well I let some of it go. A slightly moist rag and a little pressure should take it off. Most I let go until I clean the inside of the cage once a month. I do not mean leave all the feces around just some spots are to hard to get at and clean like that. Really chameleon poop seems to break down pretty fast and I personally would think there is minimual risk with it unless you just let it pile up.
