It seems the Qt custom viewport is just being updated at a slower rate. I assume this is controlled by modo and can't be adjusted by 3rd party developers.
So more info on this situation:
1) The plugin CAN set the refresh rate of the Qt version of the Octane viewport in Modo901 onwards. However I do not think this would change the situation, since the delay you are seeing is from 2)
2) Each time you change or move a mesh, adjust a vertex, change a mesh transform, change the group location transform that a mesh belongs to, etc, the plugin will reload the mesh geometry and transform. So even sliding a cube to the left results in the plugin reloading the mesh each time the transform change is detected. The plugin does this because of the way the Modo API event system works - where it fires two events for a transform change - one for the original transform position, and one for the new position, and there is no way for a plugin to determine which is which - so the plugin waits until Modo gives the signal that it has finished processing, at which point the plugin reloads the mesh and transform.
So it is not simply a matter of the plugin updating a Mesh object's Placement node in Octane when you change a transform in Modo - there are a lot of dependencies that need to be met in Modo before the change can be sent to Octane, and "waiting" for these dependencies to occur is resulting in the delay you see.
Paul