The source code of a package only contains Drools related assets like rules, functions, etc., but not processes. What you can do is either to use the binary package (you have to build the package first from Guvnor's UI) or to use the process' source URL instead of the package.
Also remember that KnowledgeBuilder doesn't throw any exception if it fails compiling a package. You have to manually check for errors after you add a resouce by using .hasErrors() and getErrors() methods.
Best Regards,