We're definitely not experts on this. It looks like contracting is not allowed, but "independent research" is. So citizens of VWP countries or those obtaining a B1 visa should be eligible to participate, but we would be unable to compensate them beyond incidental expenses (travel, food, and housing). I've updated the website to reflect this.
I'm informed @Erik Jenner beat me to this idea! Check out his version as well.
We're definitely not experts on this. It looks like contracting is not allowed, but "independent research" is. So citizens of VWP countries or those obtaining a B1 visa should be eligible to participate, but we would be unable to compensate them beyond incidental expenses (travel, food, and housing). I've updated the website to reflect this.