I have it on the way but not here yet. As far as I would guess, it's probably a lot like the Revolution since it's the same material and the Rev has no hole. The way the o2 material is made with the firm core and the softer outer layer wouldn't really lend itself to being hollow, well in my opinion anyway.
It is not bullet compatible, since there is no place to insert a bullet. If you want to make it vibrate, it looks like the wide base might carry vibration well with something like the Hitachi pressed up against it, but that might be rather unwieldy.