Even with an aviary you need to be prepared for winter. Veiled will, in the right conditions, be happy enough outsdie for much of the year (in Gauteng) during the day and at night so long as the temperature stays above 10c, to be safe allow 15c as the minimum to cater for the sudden unexpected drops.
That still leaves enough days/nights where an indoor cage is needed; which brings you back to needing seperate cages.
Natural sunlight beats artificial UV light any time, as does the free flow of air and the exposure to changing day lengths and weather patterns found outdoors. Obviously common sense and caution are needed as they are still in an artificial environment. One big problems with veileds in this country is the high night time temperatures and the 365 day constant environment, which is totally unreal.
I have not tried the BSS idea on Veiled as I think they are too big for it too work, unless a lot of time and effort is spent monitoring it carefully in the early days. This is only my opinion and is weighted by having far too many large chameleons to be able to do it properly.
I have used the BSS approach with Brookesias and Rhampholeons with good success. This was based around the use of two species of springtails and a soft woodlouse (Trichorhina tomentosa); to the best of my knowledge I am/was the only person breeding the tropical woodlouse in SA. Veiled will produce large droppings which may overwhelm springtails and probably also woodlice. Overseas I am aware that such setups exist but overseas there is a wide range of suitable organisms freely available to make it work. Locally, I think it is best to go for an easy to clean environment, which can still be very decorative.
But, as I have said, that is only my opinion and I am sure there are people currently experimenting with BSS setups on chameleons larger than Brookesias.
David
www.sa-chameleons.com