You know, this crossover makes perfect sense when you think about it. Gensokyo is a hard-to-reach mystical land of strange creatures and humans who bumble themselves around into silly adventures. Genesis under the lyricism of Peter Gabriel evoked nursery tale, Wonderland-esque pictures of the mundane and contemporary with a spritz of theatricality. Seems like a nice fit!
...But it's still weird to see two of my favorite things mashed up like this.