IIRC Octane doesn't support a 'ignore shadows' functionality right now, also it might be on the to-do list for versions to come. You could try to make a diffuse node with a texture emitter on a very low power so that it 'glows' a little and 'swallows' any shadows. Maybe that works (I once tried that for a background billboard)
Under diffuse, there is a "matte" checkbox, which I am embarrassed to say, I have never used, but it is related to shadows (I think it means shadows do not cast on it). There is a heap of info in the forums here about it.
Yes - when you change a material to be "diffuse", you get a "matte" checkbox (last pin in the tree). Search these forum for "matte" - it was introduced recently, but there have been issues with it in some Octane releases. As I say, I've never used it - sorry.
Perhaps you could post a sample of what you are trying to do? Octane is an unbias renderer, so it makes everything as realistic of possible. For a whole scene you can use the "directlighting" kernel, and then increase the oadist to kill all the shadows (about 10 should remove them all).