They're extremely tough. They have a video online where they blow up the backpack with an explosive and the bladder is still fine. The only thing is that barbed wire would probably puncture it if you dragged it into it (though I'm not sure what kind of race you're doing where you'd be forced to go through it).
If you're going to risk puncturing it, I'd go for a cheap alternative. The reason this is so expensive is that it has an inline filter so you can drink from questionable sources safely (it's more of a survival tool than a standard hydration bladder).
I got this pack when amazon had the backpack+system on sale and I can say the build quality is top notch. The pack is extremely high quality with modular parts, as is the bladder itself (you can separate each part or fill extra packs with water and swap out as needed). Definitely a step up from a competitors such as Camelbak. That being said, the bladder has a lifetime guarantee though I'm not sure if they cover intentional crossing of barbed wire...
tl;dr: You probably don't need this unless you're thru-hiking or drinking from a questionable soure. Get a cheap hydropack for the event.