Hmm, that's interesting, based on your own logic, it should be a fairly big (maybe even a slightly bigger) cheque for Marc then shouldn't it?

Not wishing any ills on the lad ,but if he was to pick up a lengthy injury , would we be responsible for his rehab still .

I think the quote from the Doc on the BBC last night was telling, he said that Hull paid more for Sneyd than he himself would have paid and that the fee was more than £100,000.

Pretty obvious based on this that we got a brilliant deal for him.

Yes, as he is still a Salford contracted player.

Is it not different for a season long loan?

I'm not sure this is a big issue.
He's currently on a relatively small contract and I would guess Cas are fully responsible because , as Red Willow rightly says, it'll be different when it's a season long loan.
If there is a problem,it would come if he was injured and not fit enough to start the season with Hull.
We could speculate all day but it really depends what the transfer documents say