Yes succulents are some of the best plants to keep with leopard geckos. Just make sure they dont have any pointy spikes on them that could harm your gecko. They can be used for your personal looks of your cage. I thought about getting one for my cage but never did and dont really have room. The only problem is leopard geckos dont like bright lights, so you may come across problems with growing them in cages because even though succulents dont need as much light as others, they still need some. So it wouldnt hurt to try. Ive read that the green ones live the longest without light. The red ones are more light hungry.
Someone suggested to me to have two succulents and rotate them in and out of the tank, when out of the tank let them be exposed to a good growing light. You will have better success at keeping them alive this way. But you could always experiment and see what works. I think without much light they will slowly die after a couple of months.
I thought this would be a way to make the cage look nice and possibly keep plants again.