ServiceMix is a container for JBI components. At the same time the ServiceMix JBI container by itself is a JBI component. This characteristic enables ServiceMix to be deployed as a standard JBI component into another vendor's ESB container, provided the host ESB container supports JBI components. When we say a ServiceMix container is a JBI component, it means that a host container (like OpenESB from Sun) can make use of almost every ServiceMix component, whether the component is a standard JBI component or a lightweight component (the difference between these two is explained in the text). The promise of this model is that the developer-created components can be reused across JBI containers.
To answer your query:
WAR, EAR, RAR or a standalone server?
ServiceMix supports integration with JOnAS, JBoss, Spring, Tomcat, Geronimo, etc. Moreover, ServiceMix is also available as a .war file which can be used to deploy ServiceMix inside any J2EE application server or Servlet Engine. This will aid the side-by-side deployment I talked about in this link.