Here's a website with information for you.
I virtually keep my panthers and my veileds the same for both the
humidity and the temperature. The basking spot is around 90F. Both
species live to be quite old for me...so it must be okay.
You need to bear in mind that where you live has an affect on the'
hydration/humidity required. If the area you live in is hot and
dry then then you might have to provide different levels of
hydration/humidity than you would if you lived in a cool moist
climate, etc. I also think that extra hydration can help to
compensate for lower humidity...up to a point.
P.S. Don't give up on finding your veiled just yet. An iguana was
lost by a neighbor of mine and it took them a month to find it.
(I realize that an iguana is bigger than a chameleon so a
chameleon would have more predators.) Then again....how bad would
it be if you ended up with two chameleons??