Yes, but only if the nodes are in the same region and availability zone. From amazon's pricing page [http://aws.amazon.com/ec2/pricing/]:

  There is no Data Transfer charge between Amazon EC2 and
  other Amazon Web Services within the same region (i.e.
  between Amazon EC2 US West and Amazon S3 in US West). Data
  transferred between Amazon EC2  instances located in 
  different Availability Zones in the same Region will be
  charged Regional Data Transfer. Data transferred between 
  AWS services in different regions will be charged as
  Internet Data Transfer on both sides of the transfer.