The past owners of Mountain Corals, Tim, Joe and Cindy always said that the rotifers were a way to deliver a bag of Velvet Green (their proprietary species of single celled algae) to the coral so that it could be useful to the coral. Rotifers can fill up with something like 10 or 20 times their weight in algae!
If you are feeding rotifers to your tank without first giving them a meal of green, then yes they are useless.
P.S. That's why rotifers are sold in a bottle of greenwater!