If someone can get vidcaps from Probst's preview (or just has good eyes and a big screen, probably), there is a brief shot of the start of the slip n slide, which I think shows everyone. Right around 50 seconds in
Meh, here's a screen cap but it's really dark and blurry at that particular point. It won't help much in identifying who's playing or not, but it does show more things about the challenge. They are definately lubing up with stuff from the two troughs. You can see a bucket sitting on the ground to apply it. It could easily just be water instead of oil as it wouldn't be good for the environment to have an oil slick on the ground :)

Also there is a big box or something sitting on the table where Bob is. Not sure how that plays in. We can also see the "sit out" bench and there are definately 2 people there, albeit mystery people.

FWIW:

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