[UPDATE]
I have looked a bit deeper into this. Using the FMOD Studio Debug overlay and the profiler in FMOD Studio and tracking the memory usage I have found out that the dialogue lines are indeed loaded separately as they are used. This is also confirmed by them being released after they are done playing which I failed to notice before. Sadly Unity’s memory profiler doesn’t seem to be able to track the memory FMOD actually uses for loading in and playing the audio clips but given the fluctuations in the total memory used by the application it seems that the information provided by FMOD is (at least for the most part) correct.
It might be worth looking into the log message created by SystemI::createSoundInternal as it is a bit misleading with its name, since it seems to be just scanning through the audio table rather than actually creating a sound.
I now consider this issue resolved so feel free to close down this topic. While I was looking into this and FMOD in general I have run into another problem though and have created a separate thread for it here: Short sounds not released after they finish playing. Any help with that issue would be greatly appreciated.