I would agree that DI injection engines can be more susceptible to carbon build up, but the sources I have read indicate that this seems to be an issue on a number of VAG cars. It would also seem to be dependent upon fuel quality and how the car is driven. I.e. short drive cycles around town and cheap supermarket fuel.
Personally I tend to try to utilise as much of the performance as is safe dependent upon road conditions and traffic with my RS on my favourite twisty B roads. The RS also only drinks 99 RON fuel.
If it was me, I would fit the Mountune part first and then if consumption was still and issue look at a catch can. As to how the 2 components would work together, logically, they shouldn’t cause an issue, but as I have no first hand experience I wouldn’t want to offer an opinion either way..