Yes - a CODM ShortcutPiston object defines a momentary virtual switch that toggles the state of a latching virtual switch (stop/coupler/tremulant). Hence if you have MIDI output configured for that latching virtual switch, then it will send its usual on/off messages when it's toggled. I.e. the result would be exactly the same as if you had toggled that virtual latching switch directly by clicking on it.
The ExampleCustomOrgan2.CustomOrgan.Hauptwerk.xml CODM ODF has some example ShortcutPiston objects to experiment with.
Hence the answers are:
I've never messed with ShortcutPiston (s) in the CODM. If a shortcut piston is defined to trigger a coupler, i.e. Great to Pedal, does the corresponding physical coupler (SAM) move to the on position?
Yes.
And just to verify, these can be engaged by momentary contact? I.E. a non-latching piston?
Yes.