I see nothing wrong with two characters of different species coming together to make a totally new species. I've seen a few crosses myself out in the game. In a Warrior Cats roleplay, there is a character that is part cat and part hyena. Odd combination, but it's unique and something different. I have also seen gryphons and dragons pairing up and having little draphons... or whatever you call their offsrping, up in Sky's Rim.
Of course, many of these pairings I see having pups, kits, and cubs wouldn't be able to do so in real life. But in the wonderful world of Feral Heart, nothing is impossible ^3^