That’s a great question. DB Sync’s OpenMRS Camel Component defines a model for each entity that it supports. Right now this model is some OpenMRS-looking JSON representation, there is no good reason for that except practicality/ease/velocity when this was initially developed.
However this model could (and should) be FHIRzed. This is something we would like to start doing progressively from here on, and surely we’ll need some guidance from @ibacher in doing so. This FHIRzation is loosely on our roadmap and @wyclif and I we already discussed that we would FHIRze a couple of entities as a POC. If you guys would like to prioritise this we would be more than happy to do it as a joint piece of work.