This looks very dubious. Basically, if you start a startup for them, they'll pay you $100k in salary, plus up to $900k more. But that is an upper bound. It's only a million dollar contest in the sense that no matter how valuable your work, they will not pay you more than a million dollars.
Also, the $900K can only come from the first year's revenues. How many sites/products will make that much in the first year? Sounds like a real ripoff.