So basically they're paying the winners less than one year's salary for a picker, in order to develop a technology that will permanently replace virtually every picker in all their warehouses. I see how this is a good deal for Amazon, not so much how it's fair for the competitors or good for the human race.
It doesn't mention anything about intellectual property, patents, etc except this bland remark: "Participants will be encouraged to share and disseminate their approach to improve future challenge results and industrial implementations."
So, it is doubtful that entry into the contest or acceptance of the prize would compromise intellectual property (trade secrets, patents, copyrights, etc) of the creators. Much as the X prize, Grand Challenge, etc did not require contestants or winners to forfeit any IP. From the look of it, Amazon is staging a contest, paying travel expenses, and offering a prize, all in lieu of executing a RFP and performing testing themselves. Still probably a win for them in the end, if one or more of the contestants is in fact a commercial robotics vendor.