Things are complicated here to explain...
In short.
As I wrote before - Blender currently has a rudimental VDB support internally. So the Octane module uses what works currently, waiting for Blender developers to finish all this.
In long.
Blender saves the VDB files with non-standard channel names. So, standalone opens these files and by default sets the "density" channel to all the Octane channels including "emission". So, because of that, by default you see the "emission" channel "working" - but it renders a wrong data.
But the things are more complicated. Blender exports the channel having this data into a VDB files, with non-standard "heat" or "heat big" names. So, if you choose it manually in standalone for Octane's "emission" channel and this Blender's "heat" channel" will have a meaningful data in it - it should be rendered by standalone.
But the thing here is: Blender only uses this channel internally for any other smoke types than "
Domain" (when the "fuel" functionality is active in there). But only "
Domain" type supports VDB grids. So, despite the fact Blender tries to save this "heat" channel when generating VDB cache, its code is not finished and the standard functionality of accessing the "flame" grid (that must use the "heat" channel data according what I see in Blender Foundation's code) is not working currently. The Octane module uses Blender's function implied to return the "flame" grid with this data, but currently (in 2.77a) it always returns empty grid (filled by zeroes). Despite the fact the same function implied to return the "density" channel works absolutely OK.
This is the Blender code (Octane-specific) you can see on GitHub:
You see here that Octane module
uses the Blender's function to access the "flame" channel, and it uses this channel as Octane's VDB "emission" channel. But as I said - Blender Foundation's
SmokeDomainSettings_flame_grid_get()
function always returns the empty "flame" channel for "Domain" type smoke. At the same time
SmokeDomainSettings_density_grid_get()
works OK and returns actual "density" grid data (used for Octane's scatter and absorption channels).
So, we need to wait before it will be fixed by Blender developers... I could implement this functionality instead of Blender developers, but I can't spend resources developing Blender itself, I only do anything regarding Octane support in it... If I developed this Blender's functionality myself, after Blender developers do the same in the same parts of Blender - merging with a new Blender versions becomes a nightmare 'cause the same functionality in the same Blender files will be developed differently...
So, as I said we need to wait for next Blender versions where the VDB support becomes improved...