Well spotted. The CMMN counterpart for the DelegateHelper was indeed not added to the CMMN engine yet. It is now: https://github.com/flowable/flowable-engine/commit/cc725d68fc29d297898838894a85a7a4ad2e0d32
You can copy the CmmnDelegateHelper class in your projects as-is (as they are static methods) and remove it with the next release.