It's totally reasonable. Reference your RouteBuilder that defines the Java DSL routes first, then any Spring routes like below.
<bean id="customerRoute" class="cc.notsoclever.examples.cxf.wsdlfirst.server.CustomerServiceRoutes">
</bean>
<camel:camelContext xmlns="http://camel.apache.org/schema/spring">
<routeBuilder ref="customerRoute"/>
<route id="bar">
<from uri="direct:bar"/>
<to uri="mock:bar"/>
</route>
</camel:camelContext>