Many KDF players may not want the Kazon, but there are those that do, and if the option is implemented in game, it's not like you HAVE to accept it.
I have ignored the appearance of the Ferasans completely (heck, they're not even a canon species, unless they are based on the other humanoid cat race from TAS!)
I was talking with some people in the fleet I'm a member of, and discussing Kazon ships. That is a no, because the Kazon have always been so technologically insuperior to the Alpha/Beta Quadrant powers. But as for members of the species in KDF crews, I don't see a problem (some of the special KDF Doffs are a bit dodgy, so whats the big deal with Boffs too?)