OSB 11.1.1.6 documentation gave the following long waited update on usage of OWSM policies to use with SwA and the same can be found in the link.
Notes:
Oracle Service Bus does not support attaching OWSM policies on proxy/business services that process messages with MIME attachments, including message protection policies with SwA (SOAP with Attachments) properties enabled. Using OWSM policies with MTOM-enabled services is also not supported.
Release 11.1.1.7 supports WS-Security with MTOM and SwA and new features are summarized here.
Siva's Blog 