You could do things this way, but it's not clear to me why you
wouldn't just use Rails' Web services.
As I understand it, AWS isn't going to disappear - it just may turn
into an add-on rather than remaining part of the core Rails package.
For those (apparently few) of us who use it, AWS is a really powerful,
elegant way of working; REST makes it simpler to create simple XML
documents, but the effort involved in turning those documents into
SOAP or XML-RPC is pretty painful if you code it yourself.