Yeah, you gotta be an IGDA member to enter. Note that they don't actually give out the prizes themselves; instead, their judges name the maps they think are best, and hand them over to Epic who may or may not decide to distribute some MSU phase 4 money to the IGDA picks, if they feel the some of the IGDA picks are better than some of the MSU phase 4 entrants.
If you read the site carefully they explain that this contest is designed to "help" IGDA members get into the MSU phase 4 contest (past the standard MSU phase 4 deadline).