Answering myself: I eventually got rid of the relocated spinjar jackson artifacts (I think I faced some Gradle cache issue) and I found this in the Camunda examples: https://github.com/camunda/camunda-bpm-examples/tree/master/spin/dataformat-configuration-global.
I wrote my own DataFormatConfigurator to add a module to the Jackson ObjectMapper, which uses the Zalando data format mapper mentioned in my question.
That did the trick!