Is this the suggested way to update revit geometry in standalone or is their an obvious and automatic way I am overlooking?
Yes, this is the best way. There is probably saome LUA code you could write to automatically plugin in the materials (check the LUA forum here - it may have already been written).
Also are there any import / export units to be considered when exporting to standalone, or is this automatic? I work in inches in REVIT and have to scale up material sizes dramatically in standalone.
OctaneRender for Revit will convert the scene into meters when loading into Octane. This should also happen when exporting to OCS/ORBX.
And, are there differences between exporting to ORBX vs OCS?
ORBX is like a zip file containing the .OCS file and all the scene assets (texturemaps, obj files, etc).
Paul