Does it matter where you use it ?
If an image is in grayscale then it uses less memory and you can use it where ever you want, it doesn't matter if you put into a Diffuse or Bump-Input.
Autodetection shoudn't be a problem, if you have no Colorvalues and only Brightnessvalues then an Image is in grayscale.
Sorry this is all Offtopic, let's first solve the Bugs of OctaneRender for Blender
