You don't need a replyChannel on your gateway; because you don't have a reply-channel on your outbound gateway, the framework knows it needs to send the reply to the gateway.
The reply queue on the rabbit template is unrelated to the framework reply channel. The reply-queue is an AMQP (rabbit) Queue on which all replies are sent. This is to avoid the overhead of creating a new queue for each reply.
It is a new feature in the 1.1.0 release that came out last week.
Gary P. Russell
Spring Integration Team
SpringSource, a division of VMware