I have a UE-script on record A that updates parent record B through record.submitFields(). There is a workflow on record B that should initiate on update on beforeSubmit with edit, direct list edit and create. The workflow on record B doesn't initiate. Is this because the WF is considered a User Event-script and the "UE can't trigger UE"-rule prevents it from initiating?

yes

There should be an initiateWorkflow method in the task module. Maybe you can use that to execute your workflow

@rustyshackles Yes, that was what we did as well. Just couldn't find anything in the help/SA to confirm my suspicion. @battk Thanks for the confirmation!