@StephenOTT , thank you for your suggestions.
I don’t want to use script task, when dealing with decision tables/rules. I would like to have clear convention, that allows users/analysts to easily read process diagrams. And for that, I need service task, always when calling back-end system, user task when calling front-end, and RuleTask when calling DMN table. No dual uses 
Regarding your pattern. I think for my case, using JavaDelegate for Rule Task would be more cleaner solution. But it’s an interesting approach you designed, and maybe I will use it later