Well the contest was open to anyone and it was very much a contest of OC skill. The specific contest rules and hardware regulations are determined by the sponsors.
Note that there was also a more public friendly precision OC category in the contest where 63 different users successfully hit the score target and many more tried (252 different registered users hit within 10 3DMarks of the target).
As to the 3DMark 11 submit number as received by Futuremark, the ballpark is easy to verify as due to our current policies most results are visible to anyone on the 3dmark.com website.
K404's calculations have an error. 43 weeks times 35000 is 1.5 million submits, not 15 million.
Current benchmark submit count is 1501261 3DMark 11 results in the database, 1470951 of which are currently visible on the 3dmark.com website.
The link to the first visible submitted result is http://3dmark.com/3dm11/103
The first result within the Gainward competition timeframe is http://3dmark.com/3dm11/1740497
The last result within the contest time period is http://3dmark.com/3dm11/1893992
So, 153495 3DMark 11 results came in during the contest timeframe, 132437 of which are currently visible to anyone on 3dmark.com.
The rest are results from unsupported version 1.0.0 (after the patch was released, older 1.0.0 results are still visible), results with pirated keys, results that have been invalidated and results hidden or deleted by users.
Feel free to look around the results by changing the ID if you want some verification that there are indeed as many results as stated.