At present time, Octane is a stand alone renderer and there is no chance to integrate it. I don´t know if it is planed to support a render integration in a 3d app...
Softimage has an option to host an external application in its viewports and maintain a live link with it. Unfortunately, from what i understand, it requires the application to include some lines to make XSI recognize it. It would be awesome if someone managed to accomplish integration this way.
for my modest opionion, all the time that is used to create the plug in, should be used at the same way to integrate in the viewport (See post up) the render. But, of course, is just a dream. But thinking good, is not a bad idea. Thank any way to radiance for his patience