I’m sure I could borrow a DK2 off of a friend to test it, but it uses a similar Skydome style to the default UE4 system. I haven’t seen any issues with it yet, and one of the teams at work is using a DK2 with the standard UE4 skydome. I don’t see any reason why it wouldn’t work for VR, though I’m not explicitly aiming for it. I can test it though, and perhaps make a template suitable for VR users. You’ll need a beefy GPU either way I expect.
Performance hit is scalable, it really depends how many of the features you want to plugin. The Surface shaders add considerable instruction counts, and although the weather planes are very well LOD’d, they still take up a big chunk of screen space with a translucent material. That’s just the nature of the beast really.
Currently, there are no ‘seasons’ built in as such, but you can create one of your own just by changing the parameters. The Weathers’ AI Engine can select random weather patterns that follow after each other.