Would it be possible to build your big cage with some sort of divider in it so that they can't directly get at each other? Unless a vorax is just a huge variety of gecko (I'm not familiar with it), I would think that the chameleon might try to eat it. Even if they are the same size, they might well fight; nocturnal/diurnal doesn't mean they'd never bump into each other, just that they'd mostly not bother each other. I guess to me it just seems risky, especially with what I've heard about chameleons being very vulnerable to stress.
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0.1 Albino Leopard Gecko - Tigger
0.1 Crested Gecko - Pooh-Bear