I was reading about it a little while ago. As I understand it, there is a licence you need to purchase if you’re using it for commercial releases. However, the licence only applies to the use of content that comes with Bryce. In other words, it can be used freely as long as you’re making your own renders.
I believe you can export .obj files and whatnot, or at least you can in Bryce 7. The main hurdle is that it takes hours to get a high quality render at a resolution that would be suitable to use as a game background, but I guess if you’re not making tons of them it’s probably doable.
Just a thought anyway, love the aesthetic.