Lux, Vue is using a gpu/cpu interactive path tracer. http://www.e-onsoftware.com/products/vue/vue_2016_complete/?page=14

If y ou look at the recommended system specs to run Vue, they say they are using Opengl, and require an Opengl accelerated video board for optimal compatibility. They also give a warning at the bottom of the page that using Nvidia's Optimus or ATI's BinaryGFX technologies will present severe Opengl problems. So does that mean they're using Opengl instead of Opencl or cuda?

It looks like a lot of the advanced rendering features in Vue are crippled in the path tracer too. It seems very primitive and only good for quick preview or viewport rendering. I don't think clouds are even supported in Vue's path tracer yet.