I think I found something that unwraps for UNREAL...
https://www.thefoundry.co.uk/products/mari/learn/
the 1st video.
What do you mean? AFAIK, MARI is a texture painting software that requires already unwrapped model to work with. It just creates textures and exports them to be straight forward compatible when used with UE4 (presets for roughness, metallic, etc.).
It probably has some internal quick unwrap generator like most of texture painting programs (Substance, Quixel, etc.), but not sure why would it be specifically good for Unreal?
Or am I missing something? :S