Do dolphins really sleep?
I'd say that unihemispheric sleep and adaptations like it really are sleep - the brain activity on one side of the brain gives a characteristic sleep pattern.  It certainly must satisfy the needs of an aquatic mammal like a dolphin or a whale since they have to be partially conscious to breathe by surfacing regularly. 

It does seem to affect the brain physiology, but is there a reason you would not call it sleep?