Yes, this is possible exactly the same way. You are not using ReWire, in this case. ReWire transfers audio data from one application to another one, not MIDI. And ReWire is also using for syncing of transport commands. In this case, you are using Mac OS X native virtual MIDI port: IAC bus.
So in Notion, select the IAC Driver as an output. In Cubase, set IAC Driver as an input.
To use ReWire for transport commands (and syncing):
Launch Cubase first.
Then launch Notion (or another ReWire slave software).
In Devices menu of Cubase, select the ReWire software.
Now, you can route output buses of the ReWire slave application to Cubase.
ReWire does also transfer MIDI data from one application to another, the protocol allows for it. Not all applications have it implemented, but (for instance) I use it with MAX/MSP all the time.
In case of the question by the OP, if Notion doesn’t have Rewire available - or specifically MIDI over ReWire - the using a MIDI-routing software like MIDI-OX would probably be the easiest way to achieve the necessary routing. (Notion MIDI IN > MIDI-OX > Cubase MIDI IN).
Thanks, all for the replies. I’ve tried repeatedly to do just what has been described, using IAC ports for MIDI out from Notion to MIDI in to Cubase, with no luck. It just won’t work. Frustrated!