If I may chime into the discussion. My first cham was an ambanja who I had for nearly 4 years. When he was 3 1/2 I bought a baby male veiled (he was 6 weeks old when I got him and was quite the tiny little guy). Their cages were next to each other and they could see each other. I felt that since the veiled was so small, and not sexually mature in the least that it wouldn't present any problems at all.
Within 2 1/2 months, my ambanja was dead. There was nothing at all changed in his care, and he had always been perfectly healthy. He had been spending more time towards the back of his cage, but by the time I realized that there might be a problem he was too far gone with stress. He NEVER fired up, he just got to the point where he was extremely dehydrated - I showered him for an hour at a time in the shower, but it didn't help. We went to the vet and he died that night. It crushed me, but it taught me a valuable lesson - chams may not demonstrate they are upset/stressed, but I will never allow 2 chams to see each other on a constant basis such as that. I hope this helps at least one chameleon because then Kibi won't have died in vain.