I think I might be able to answer my own question. If there is no need for reuse for the bean for other Switchyard services, a bean can be mapped with @Bean("beanName") and it can be therewith used. What might be spec-nonconformant is that if there is no explicit name in the @Bean annotation, that Camel does not recognize the class name as a bean name, but I am not sure.
If you want to invoke Java classes with no requirement for providing a service contract, then just use CDI beans. You can invoke these directly from a Camel route by using @Named on the Java class you want to invoke and beanRef("YourBeanName") or to("bean://YourBeanName") in the route itself.