I won't buy anything with actual soap in it.
And with lemongrass, cedarwood, eucalyptus, and geranium in it, it appears to be a type of flea shampoo though I don't see it saying that at the site. Plus, just to be safe, I'd not use it on ANYTHING in a "cat house" (no pun intended) just because there's a warning that it's not for cats. Seeing the word geranium makes me kind of skeptical--almost as much as pyrethrins does. Especially if you're already using a top-spot type of flea and tick control since a lot of the brands contain pyrethrins.
You might want to read this:
http://www.drjeffnichol.com/?p=2904Edit: Incidentally, Castile Soap isn't exactly the same thing as other soap, but it's still soap, so I won't put it on dog skin. It was developed for humans, not dogs.