(*is saddened that the rephrasing of Kirk's famous line, "What does God need with a starship?", seems to have flown over the heads of all the other forumites at Warp 14 speed*)
Blayyde: The Caitians would have to be flagged with the KDF icon in order to be purchased by the Klingos. Cait is a Federation member, y'know. Until they are otherwise flagged, only the decent folk of the Federation may have Kitty Krew. The ebil empire has to go with. After all, privation is a virtue to the stoic Klingos.
More Mew-Mew *and* Pew-Pew! :p
Actually, I got it first time.
And Joined Trill can be KDF Captains, even though they are members of the Federation, so there is not really an exclusivity. It's just worked out that way so far. There are also the Liberated Borg, although they were formerly Human for Federation and Klingon for KDF so that doesn't really count.
My idea, though, is that the Klingon "Catians" would not be Caitians. They're something else. An offshoot, or rebel group. Like Vulcans and Romulans. For one thing, right now you can't play a Caitian Captain in the KDF, so there you go.