IntelliTrace do not support attaching to a already running process, you need to launch the process either from Visual Studio or from command line with IntelliTrace to monitor it. Also mix mode debugging (debug both Native and Managed code) isn't supported by IntelliTrace.
Note that assemblies loaded by Assembly.LoadFrom() will still be monitored by IntelliTrace so long as IntelliTrace is properly enabled on the loader process. In you case IntelliTrace will decide not to monitor anything.