Quote from the Voxel Farm website:
We are working on an Unity integration, however we do not have a generic Unity plugin today. If your game runs on Unity, you will need to adapt the Voxel Farm Engine's output into your Unity project. Of course we can help throughout the process as this is something we have done before.
I've also read that EverQuest Next Landmark is using the Voxel Farm engine (although the EQN website says it's using the ForgeLight Engine, so I don't know if that's true), and the possibilities seem to be endless. Very impressive to see what people already created there.