In integrating non-SAP applications to SAP, under what situations is it advisable to use a third party middleware (eg IBM MQSeries), as opposed to SAP RFCs & BAPIs?
There is no "opposed to" to this. The preferred SAP interfaces are BAPIs/non-BAPI RFMs for synchronous and IDocs for asnchronous update. 3rd party middleware uses these interfaces and provides additional functionality (like a persistent queue in the case of MQSeries).
This was first published in May 2002