It seems that the druids may have never needed the tree to do this since they can still enter it, even after the tree was damaged enough to remove Nozdormu's blessing. Also, according to War of the Ancients, Malfurion Stormrage was able to enter the Emerald Dream before Nordrassil was created.
But the most important blessing came from Nozdormu; which ensured that so long as the tree existed the night elves would remain immortal. This would ensure that even the most corrupt of night elves would be drawn to protect the tree.