DeltaSpike container control API is only used to bootstrap Camel CDI in Java SE either directly with the Main class or via the Camel Maven plugin. Hence that dependency should be declared optional so that dependent projects that uses Camel CDI in non SE environments do not have to deal with it. This is the case of WildFly Camel for example. Note that the DeltaSpike container control packages are already excluded form OSGi imports.
As the Camel Maven plugin does not check for optionality when adding CDI extra plugin dependencies (when useCDI is set to true), it is safe to declare that dependency optional.