By rule, Risen Reef places a card into your hand. It does not draw cards. Currently, if you have no cards in deck, and you still have Risen Reef triggers on the stack, it views it as a deck out.

I used a loop with Omnath, Locus of Rage, with Risen Reef to get loads of 5/5 elementals. I decked out before I was able to give them haste.