paintable silicone caulking at shower ceiling joint?
It doesn't really matter if the ceiling joints are caulked with silicone or not.   Silicone is used so that water does not enter.   Most good latex caulks would handle this joint just as well because there isn't direct water pressure - I understand you have steam and splashes.   

My advice would be to use a latex caulk that matches ceiling color (hopefully white!) and not paint it.   Painting even paintable caulk will not last above a shower so why do it?  I also actually prefer latex here as I feel I can apply latex thinner and smoother in a corner leaving less chance for peeling in the future.   Silicone is just fine too just my preference - even when being careful you will smear silicone more and end up with larger lines more susceptible to damage later on.   (I used latex above my shower in current home and 8 years later looks brand new)