Hello:
Well, maybe Cayso may be considered by some as a kind of "gentle hunter" because he will not make any harm to his leaf-eater friends... but if he finds a bully of some kind or a bad guy... well, he is not as nice as Chomper.
Maybe Chomper (and perhaps Ruby too) met Cayso or his brother Racnar at some point, that can help too.... Racnar sounds good because he is even younger than Cayso, making him a bit more closer to Chomper.
- Off topic: About Worf, I cannot be sure, maybe he was convinced (as all of the other actors) to appear in all films, but it appears that they were all happy to make them. But Worf did sign a contract to participate in DS9 after TNG ended.