On the contrary, I have seen an adult giant day gecko and adult Diego Suarez panther chameleon kept together...
This was accidental of course, the Phelsuma got out and made his new home in the panther's cage. The guy keeping them said the panther hasn't tried to eat him..
Now, I don't know how long they were kept together, but it was long enough that the panther would have seen the Phelsuma.
If it's a large, full grown adult crested gecko, and a female veiled, or smaller male veiled, then I don't think there'd bee much harm.
They are active at opposite times of the day as well, so there'd be little to no stress.