You can indeed not access properties or otherwise read much information about the music. But it is possible to input music generated externally into Dorico using scripting. A gentleman in Dresden is doing a very interesting project that makes use of the Lua API to automate some very complex polytempo note input with material that he is generating externally.
We do have plans to enrich Dorico’s scripting API, but it’s a big job and we want to be sure we can devote the necessary time to it in order to come up with a clean, well-structured API. This is something we will hopefully be able to work on in the relatively near future, but we need a longer product cycle to make headway in this area.