Look, I don't know who's read the story or not, but it's about a master 
hunter who is suddenly thrown into the ultimate reversal.  He's not some sort 
of wuss-- he's spent his whole life hunting.  So when he meets General Zaroff 
(I'm not sure I spelled that right, it's been a while) he's totally blown 
away by the guy's skills. 
Therefore, there's no reason not to use Ranma, Ryoga, Shamps, or the whole 
gang.  Worried about 'em swimming away?  Pirahnas.  Gators.  Make up 
something.
As for Ranma being undefeatable, as far as I'm concerned, he gets shot/blown 
up/gassed/impaled/decapitated/whatever he DIES.  Just because he's a martial 
artist doesn't make him immortal.  The same goes for any of the cast.  I 
mean, sure you can drop a brick wall on Ryoga in the manga, but that's all in 
the name of comedy, anyway.
IMO, I would let the whole cast loose on the island, without them knowing the 
others are there.  If you wanna go dark, let the guy kill a few of them, or 
have them accidentally kill each other.  At the end of "The Most Dangerous 
Game" the only way Our Hero made it off was by basically going feral and 
hunting down Zaroff in his own home.  I do think this is a great idea, and I 
hope someone decides to do it.  But remember, don't forget the evil hunting 
hounds!

Kerrie