I'm not sure about this one. It may offend.
You get a charity request where the requestor is doing something difficult or dangerous in return for a donation. Should that make you more likely to contribute than just shaking a collection tin? I'd say yes, the arduous task shows genuine commitment to the cause, it is an indicator that the cause is genuinely a worthy one.
But, and this is the slightly troublesome bit, a lot of people actually pay their own money to perform directly comparable tasks, whether running in marathons or scaling new heights. So if you know that the requestor is using the donation to facilitate what is basically their hobby anyway, should you be wary?
On balance I'd say it doesn't matter. Even if the first x of the collection goes to fund the event and everything above that goes to the charity, then it's still worthwhile. That's obviously the case if x is only a small fixed sum but it's still the case even if x is a significant percentage; because it still leaves a contribution to charity which would not otherwise be raised, the requestor's task is only a side effect to the primary cause.
However let's go one step too far. Maybe that side effect is not a hidden cost but actually a hidden benefit. We don't actually care for most of the charities that solicit donation. But we do tend to care for the people who are requesting the donation. Perhaps we are simply more willing to help pay for a friend's adventure than for an anonymous sufferer's cure?