To exand a little more, in MetaMatrix we supported source calls that returned xml through:
SOAP
-doc literal/doc literal wrapped
-rpc
HTTP
-post with dynamic xml document as the content
-get with a single parameter / dynamic xml document value
-post "
-get with dynamic parameter values
-post "
All of the consumption is at the message level, there is no expectation that generated object models, or in many cases even wsdls are available at runtime. There was also a variety of security (predominately basic auth) and ws-* options supported depending up the actual call.
Ideally all transport and environmentally dependent information would be held externally to the Teiid configuration. Utilizing ESB functionality (as opposed to, or in addition to) standard AS is fine too. Out of the box though ESB does not support the latter 4 HTTP invocation modes, since it expects http routers to have their query strings pre-configured.