A good buddy of mine is a personal injury lawyer, so I've had a lot of debates with him on the nature of personal responsibility when he tells me about interesting cases he's working on. I usually fall on the side of people taking responsibility for themselves rather than blaming it on other people.
But a takeaway I've gotten from our talks is that business owners have a legal responsibility to provide a safe environment. Doesn't matter is your have people sign waivers or not. A business owner for example, can't have you sign a waiver to go running around on a driving range while people are trying to hit you with golf balls. You're gonna get hit in the head. Yes, you should be smart enough to not do this type of activity, but a business owner also cannot put you in that situation. It's not the wild west where anything goes as long as you can get someone to sign a waiver.
So think about it from that perspective. What (reasonable) responsibility does Nike have as a business to make their event a safe one? Proper safety gear, guides who know what they're doing, and a trail that has been carefully chosen all seem like reasonable safeguards. It is not overly burdensome to expect Nike to provide these things.
Just my two cents.