In the past, at least, the engine would respect a supplied iProgressMeter for some aspects of loading (calculating lights, etc.). I don't have the sources in front of me, at present, to check if this is still the case.
Yes but unfortunatelly that is only used during lighting calculation which will typically not occur in released games (it will be precalculated). In the future we should contemplate some other way to get progress from the loader.
Greetings,