That is an interesting problem. You might benefit from putting a light meter in there and seeing what it says. I'm not sure where one draws the line for low or medium light... for me the latter would include indoor succulents which get to see the sun for hours a day, so maybe artificial light would be a step beyond that, depending on the intensity. That's a range where desert cacti and many succulent Euphorbias just fail. Cross those two groups off your list.
Maybe epiphytic cacti would be viable (like the holiday cacti and a few others). Jades tend to stretch in low light (perhaps outgrowing the space) and they become unable to support their own weight, over the course of a couple of years. They can be maintained with regular pruning, but it isn't what I could consider a pretty sight.
Haworthias might work for you. I can only guess because my plants have never experienced low light.
The other genus that's usually mentioned in the same breath is Sansevieria, where you have a number of options for shape and size beyond the usual mother in law's tongue types. The trailing succulents like the donkey tail (Sedum burrito or morganianum) and the rosary plant (Curio rowleyanus, formerly a Senecio) do well in lower light outside, so they might tolerate a bright location indoors. Just guessing there.
One thing that's going to be hard for many succulents in a vivarium is the lack of airflow. Depending on the attendant (airborne) humidity, fungal problems can get the upper hand when there's poor ventilation. That's one reason why succulent terraria and similar enclosed environments often fail.
Do geckos like heat lamps, or heat-generating (incandescent) lamps? I would think that could be quite stressful for many succulents, and not a good way to generate their light.
Thank you for the help... again! 
