You are probably aware of the OMG DDSI specification which defines the wire protocol for DDS. You can find it at http://www.omg.org/docs/ptc/08-06-13.pdf . So the most important prerequisite for interoperability is available. However, I do not know which vendors have implemented DDSI and I am pretty sure there are no real-life examples of systems that actually exploit interoperability between vendors. This might change in the coming year though, because DDSI is a relatively new standard.