There isn't swag in this hackathon, but there are a LOT of opportunities to win cash prizes. Check out the homepage for the full list. In addition to the 1st - 10th place winners, there are cash prizes on the line for an additional 30 submissions with the Silver and Bronze prizes.
There is no limit to how many you can submit! There's only a limit to how many prizes:
Each Maker may only win one of the top 10 Overall Ranked Prizes regardless of the number of eligible Submissions they submit. A Maker may win a Top 10 Overall Ranked Prize and additional Silver, Bronze, and Bonus Prizes for different eligible solutions.
Basically, you can only win one of the 1st-10th place prizes for a single submission, but your other entries may be able to win the other prizes. The entries just need to be unique.